diff --git a/frontend/src/components/ExportDataModal.jsx b/frontend/src/components/ExportDataModal.jsx
index d8cc000..c97eedc 100644
--- a/frontend/src/components/ExportDataModal.jsx
+++ b/frontend/src/components/ExportDataModal.jsx
@@ -2,10 +2,7 @@ import React, { useEffect, useMemo, useState } from 'react';
 import { experimentsApi } from '../api/client';
 import Button from './ui/Button';
 import Alert from './ui/Alert';
-import {
-  EXPORT_DIMENSIONS, dimLabel, otherDimension,
-  listDimensionMembers, buildMatrix, toCSV, csvFilename,
-} from '../lib/dataExport';
+import { listExportableParams, buildSubjectSeriesMatrix, toCSV, csvFilename } from '../lib/dataExport';
 
 const PARAM_GROUP_LABELS = { metrics: 'Session metrics', daily: 'Daily record fields' };
 
@@ -28,9 +25,8 @@ export default function ExportDataModal({
   const [error, setError] = useState(null);
   const [statuses, setStatuses] = useState([]);
 
-  const [rowDim, setRowDim] = useState('date');
-  const [colDim, setColDim] = useState('subject');
-  const [pinnedId, setPinnedId] = useState(null);
+  const [xField, setXField] = useState('__date__');
+  const [dataId, setDataId] = useState(null);
   const [groupBy, setGroupBy] = useState(() => {
     const valid = groupField === '__none__' || groupField === '__name__' || groupField === '__id__'
       || subjectTemplate.some((f) => f.active && f.fieldId === groupField);
@@ -48,42 +44,38 @@ export default function ExportDataModal({
     return () => { alive = false; };
   }, [experimentId]);
 
-  const pinnedDim = otherDimension(rowDim, colDim);
-  const subjectIsAxis = rowDim === 'subject' || colDim === 'subject';
-  const effGroup = subjectIsAxis ? groupBy : '__none__';
-  const ctx = useMemo(() => ({ statuses, animals, dailyTemplate }), [statuses, animals, dailyTemplate]);
+  const params = useMemo(() => listExportableParams(dailyTemplate, statuses), [dailyTemplate, statuses]);
+  const effDataId = dataId ?? params[0]?.id ?? null;
+  const dataParam = params.find((p) => p.id === effDataId) ?? params[0] ?? null;
 
-  // Members of the pinned dimension populate its value dropdown.
-  const pinnedMembers = useMemo(
-    () => listDimensionMembers(pinnedDim, { ...ctx, groupField: effGroup }),
-    [pinnedDim, ctx, effGroup],
-  );
-  const effPinnedId = pinnedId ?? pinnedMembers[0]?.id ?? null;
-  const pinnedMember = pinnedMembers.find((m) => m.id === effPinnedId) ?? pinnedMembers[0] ?? null;
+  const activeDaily = useMemo(() => (dailyTemplate ?? []).filter((f) => f.active), [dailyTemplate]);
+  const xOptions = useMemo(() => [
+    { id: '__date__', label: 'Date' },
+    { id: '__days__', label: '# Days Reach' },
+    ...activeDaily.map((f) => ({ id: f.fieldId, label: f.label })),
+  ], [activeDaily]);
 
   const matrix = useMemo(
-    () => (pinnedMember
-      ? buildMatrix({ rowDim, colDim, pinnedMember, groupField: effGroup }, ctx)
-      : { columns: [], rows: [], context: { label: '', value: '' }, corner: '', groupAxis: null }),
-    [rowDim, colDim, pinnedMember, effGroup, ctx],
+    () => (dataParam
+      ? buildSubjectSeriesMatrix({ xField, dataParam, groupField: groupBy }, { statuses, animals, dailyTemplate })
+      : { columns: [], rows: [], context: { label: 'Data', value: '' }, corner: '', groupAxis: null }),
+    [xField, dataParam, groupBy, statuses, animals, dailyTemplate],
   );
   const hasData = matrix.rows.length > 0;
 
-  // When the user changes an axis, keep the two distinct and reset the pinned pick.
-  function changeRowDim(next) {
-    setRowDim(next);
-    if (colDim === next) setColDim(otherDimension(next, null) ?? EXPORT_DIMENSIONS.find((d) => d.dim !== next).dim);
-    setPinnedId(null);
-  }
-  function changeColDim(next) {
-    setColDim(next);
-    if (rowDim === next) setRowDim(EXPORT_DIMENSIONS.find((d) => d.dim !== next).dim);
-    setPinnedId(null);
-  }
+  const groupedParams = useMemo(() => {
+    const out = [];
+    for (const p of params) {
+      let g = out.find((x) => x.group === p.group);
+      if (!g) { g = { group: p.group, items: [] }; out.push(g); }
+      g.items.push(p);
+    }
+    return out;
+  }, [params]);
 
   function handleExport() {
-    if (!hasData || !pinnedMember) return;
-    triggerDownload(csvFilename(experimentTitle, pinnedMember.label), toCSV(matrix));
+    if (!hasData || !dataParam) return;
+    triggerDownload(csvFilename(experimentTitle, dataParam.label), toCSV(matrix));
     onClose();
   }
 
@@ -96,66 +88,46 @@ export default function ExportDataModal({
   );
 
   const selectCls = 'w-full border border-gray-200 rounded px-2 py-1.5 text-sm bg-white focus:outline-none focus:ring-1 focus:ring-indigo-400';
-  const colOptions = EXPORT_DIMENSIONS.filter((d) => d.dim !== rowDim);
 
   return (
     <div className="space-y-4">
       <p className="text-sm text-gray-500">
-        Choose what goes on the rows and columns. The remaining dimension is fixed to one value, shown at the top of the file.
+        One value per subject over an X axis — each column is a subject, each row an X value. Blank where a subject has no value.
       </p>
 
-      <div className="grid grid-cols-2 gap-3">
-        <div>
-          <label htmlFor="export-rows" className="block text-xs font-medium text-gray-500 mb-1">Rows</label>
-          <select id="export-rows" value={rowDim} onChange={(e) => changeRowDim(e.target.value)} className={selectCls}>
-            {EXPORT_DIMENSIONS.map((d) => <option key={d.dim} value={d.dim}>{d.label}</option>)}
-          </select>
-        </div>
-        <div>
-          <label htmlFor="export-cols" className="block text-xs font-medium text-gray-500 mb-1">Columns</label>
-          <select id="export-cols" value={colDim} onChange={(e) => changeColDim(e.target.value)} className={selectCls}>
-            {colOptions.map((d) => <option key={d.dim} value={d.dim}>{d.label}</option>)}
-          </select>
-        </div>
-      </div>
-
       <div>
-        <label htmlFor="export-pinned" className="block text-xs font-medium text-gray-500 mb-1">
-          Fixed: {dimLabel(pinnedDim)}
-        </label>
-        <select
-          id="export-pinned"
-          value={effPinnedId ?? ''}
-          onChange={(e) => setPinnedId(e.target.value)}
-          className={selectCls}
-        >
-          {pinnedDim === 'parameter'
-            ? groupParamMembers(pinnedMembers).map((g) => (
-                <optgroup key={g.group} label={PARAM_GROUP_LABELS[g.group] ?? g.group}>
-                  {g.items.map((m) => <option key={m.id} value={m.id}>{m.label}</option>)}
-                </optgroup>
-              ))
-            : pinnedMembers.map((m) => <option key={m.id} value={m.id}>{m.label}</option>)}
+        <label htmlFor="export-x" className="block text-xs font-medium text-gray-500 mb-1">X axis (rows)</label>
+        <select id="export-x" value={xField} onChange={(e) => setXField(e.target.value)} className={selectCls}>
+          {xOptions.map((o) => <option key={o.id} value={o.id}>{o.label}</option>)}
         </select>
       </div>
 
-      {subjectIsAxis && (
-        <div>
-          <label htmlFor="export-group" className="block text-xs font-medium text-gray-500 mb-1">Group by</label>
-          <select id="export-group" value={groupBy} onChange={(e) => setGroupBy(e.target.value)} className={selectCls}>
-            <option value="__none__">— None —</option>
-            <option value="__name__">Name</option>
-            <option value="__id__">Subject ID</option>
-            {subjectTemplate.filter((f) => f.active).map((f) => (
-              <option key={f.fieldId} value={f.fieldId}>{f.label}</option>
-            ))}
-          </select>
-        </div>
-      )}
+      <div>
+        <label htmlFor="export-data" className="block text-xs font-medium text-gray-500 mb-1">Data (cells)</label>
+        <select id="export-data" value={effDataId ?? ''} onChange={(e) => setDataId(e.target.value)} className={selectCls}>
+          {groupedParams.map((g) => (
+            <optgroup key={g.group} label={PARAM_GROUP_LABELS[g.group] ?? g.group}>
+              {g.items.map((p) => <option key={p.id} value={p.id}>{p.label}</option>)}
+            </optgroup>
+          ))}
+        </select>
+      </div>
+
+      <div>
+        <label htmlFor="export-group" className="block text-xs font-medium text-gray-500 mb-1">Group by</label>
+        <select id="export-group" value={groupBy} onChange={(e) => setGroupBy(e.target.value)} className={selectCls}>
+          <option value="__none__">— None —</option>
+          <option value="__name__">Name</option>
+          <option value="__id__">Subject ID</option>
+          {subjectTemplate.filter((f) => f.active).map((f) => (
+            <option key={f.fieldId} value={f.fieldId}>{f.label}</option>
+          ))}
+        </select>
+      </div>
 
       <p className="text-xs text-gray-400">
         {hasData
-          ? `${matrix.rows.length} ${matrix.corner.toLowerCase()}${matrix.rows.length !== 1 ? 's' : ''} × ${matrix.columns.length} ${dimLabel(colDim).toLowerCase()}${matrix.columns.length !== 1 ? 's' : ''}`
+          ? `${matrix.rows.length} row${matrix.rows.length !== 1 ? 's' : ''} × ${matrix.columns.length} subject${matrix.columns.length !== 1 ? 's' : ''}`
           : 'No data for this selection yet.'}
       </p>
 
@@ -166,14 +138,3 @@ export default function ExportDataModal({
     </div>
   );
 }
-
-// Group parameter members by their .group for <optgroup> rendering, preserving order.
-function groupParamMembers(members) {
-  const out = [];
-  for (const m of members) {
-    let g = out.find((x) => x.group === m.group);
-    if (!g) { g = { group: m.group, items: [] }; out.push(g); }
-    g.items.push(m);
-  }
-  return out;
-}
diff --git a/frontend/tests/ExportDataModal.test.jsx b/frontend/tests/ExportDataModal.test.jsx
index 7c866c9..2cdd755 100644
--- a/frontend/tests/ExportDataModal.test.jsx
+++ b/frontend/tests/ExportDataModal.test.jsx
@@ -12,8 +12,9 @@ const animals = [
   { id: 'a2', animal_name: 'Beta', animal_id_string: 'R-002', subject_info: { grp: 'Drug' } },
 ];
 const statuses = [
-  { animal_id: 'a1', date: '2026-07-01T00:00:00.000Z', analysis_summary: { total: 5 } },
-  { animal_id: 'a2', date: '2026-07-01T00:00:00.000Z', analysis_summary: { total: 9 } },
+  { animal_id: 'a1', date: '2026-07-01T00:00:00Z', analysis_summary: { total: 5, success_rate: 0.5 } },
+  { animal_id: 'a1', date: '2026-07-02T00:00:00Z', analysis_summary: { total: 7, success_rate: 0.7 } },
+  { animal_id: 'a2', date: '2026-07-01T00:00:00Z', analysis_summary: { total: 9, success_rate: 0.9 } },
 ];
 const subjectTemplate = [{ fieldId: 'grp', label: 'Group', active: true }];
 
@@ -22,12 +23,9 @@ beforeEach(() => {
   client.experimentsApi.getDailyStatuses.mockResolvedValue(statuses);
 });
 
-// Intercepts the Blob passed to URL.createObjectURL during handleExport so tests
-// can inspect the actual CSV text produced, rather than inferring it from the
-// <select>'s DOM value (which can be misleading — see the coercion test below).
-// Also stubs anchor .click() — jsdom treats a real click on an <a href="blob:...">
-// as a navigation attempt, which it doesn't implement; that throws asynchronously
-// (after the test has moved on) and can flakily fail an unrelated later test.
+// Intercept the Blob handed to URL.createObjectURL so tests can read the real CSV.
+// Also stub anchor.click() — jsdom treats a click on <a href="blob:..."> as an
+// unimplemented navigation that throws async and can flake a later test.
 function mockDownload() {
   let blob = null;
   const origCreate = global.URL.createObjectURL;
@@ -38,12 +36,8 @@ function mockDownload() {
   window.HTMLAnchorElement.prototype.click = jest.fn();
   return {
     getBlob: () => blob,
-    // handleExport schedules `setTimeout(() => URL.revokeObjectURL(url), 0)`; flush
-    // that pending macrotask before unmocking, or it fires after restore() has put
-    // back the (non-existent, in jsdom) original revokeObjectURL and throws async —
-    // an error jest attributes to whatever test happens to run next.
     restore: async () => {
-      await new Promise((r) => setTimeout(r, 0));
+      await new Promise((r) => setTimeout(r, 0)); // flush handleExport's setTimeout revoke
       global.URL.createObjectURL = origCreate;
       global.URL.revokeObjectURL = origRevoke;
       window.HTMLAnchorElement.prototype.click = origClick;
@@ -76,61 +70,44 @@ function renderModal(props = {}) {
 }
 
 describe('ExportDataModal', () => {
-  it('defaults to Rows=Date, Columns=Subject and shows the preview', async () => {
+  it('renders X / Data / Group by pickers; X defaults to Date', async () => {
     renderModal();
-    expect(await screen.findByLabelText('Rows')).toHaveValue('date');
-    expect(screen.getByLabelText('Columns')).toHaveValue('subject');
-    await waitFor(() => expect(screen.getByText(/1 date.*2 subjects/i)).toBeInTheDocument());
-  });
-
-  it('hides the Group by control until Subject is an axis', async () => {
-    renderModal();
-    await screen.findByLabelText('Rows');
-    // subject is a column by default -> Group by visible
-    expect(screen.getByLabelText('Group by')).toBeInTheDocument();
-    // move subject off both axes: Rows=Date, Columns=Parameter -> subject pinned
-    fireEvent.change(screen.getByLabelText('Columns'), { target: { value: 'parameter' } });
-    await waitFor(() => expect(screen.queryByLabelText('Group by')).not.toBeInTheDocument());
-  });
-
-  it('keeps row and column dimensions distinct', async () => {
-    renderModal();
-    const rows = await screen.findByLabelText('Rows');
-    fireEvent.change(rows, { target: { value: 'subject' } }); // collides with column=subject
-    await waitFor(() => expect(screen.getByLabelText('Columns')).not.toHaveValue('subject'));
-  });
-
-  it('defaults Group by to None when groupField is __none__, and the exported CSV has no Group row (Issue-1 regression guard: default export reproduces today\'s export)', async () => {
-    const dl = mockDownload();
-    renderModal({ groupField: '__none__' });
-    await screen.findByLabelText('Rows');
+    expect(await screen.findByLabelText('X axis (rows)')).toHaveValue('__date__');
+    expect(screen.getByLabelText('Data (cells)')).toBeInTheDocument();
     expect(screen.getByLabelText('Group by')).toHaveValue('__none__');
-    await waitFor(() => expect(screen.getByText(/1 date/i)).toBeInTheDocument());
+    await waitFor(() => expect(screen.getByText(/2 rows × 2 subjects/i)).toBeInTheDocument());
+  });
+
+  it('default export (X=Date, Data=Total attempts) has subject columns, date rows, blank where missing', async () => {
+    const dl = mockDownload();
+    renderModal();
+    await screen.findByLabelText('X axis (rows)');
+    await waitFor(() => expect(screen.getByText(/2 rows/i)).toBeInTheDocument());
     fireEvent.click(screen.getByText('Export CSV'));
     const text = await readBlobText(dl.getBlob());
-    expect(text).not.toMatch(/^Group,/m);
+    expect(text).toBe('Data,Total attempts\n\nDate,Alpha,Beta\n2026-07-01,5,9\n2026-07-02,7,');
     await dl.restore();
   });
 
-  it('defaults Group by to the saved field when it is a valid active subject field', async () => {
-    renderModal({ groupField: 'grp' });
-    await screen.findByLabelText('Rows');
-    expect(screen.getByLabelText('Group by')).toHaveValue('grp');
-  });
-
-  it('coerces Group by to None when the saved field no longer exists in subjectTemplate, so the export carries no stray Group row (Issue-2 guard)', async () => {
-    // Note: asserting the <select>'s DOM .value here would be misleading — React's
-    // controlled <select> falls back to selecting the first <option> ("__none__")
-    // whenever the given value matches no option, regardless of whether the
-    // component actually validated/coerced its internal state. So we assert the
-    // real behavioral effect (the exported CSV) instead.
+  it('switching X to # Days Reach makes rows the day ordinals', async () => {
     const dl = mockDownload();
-    renderModal({ groupField: 'ghost-field' });
-    await screen.findByLabelText('Rows');
-    await waitFor(() => expect(screen.getByText(/1 date/i)).toBeInTheDocument());
+    renderModal();
+    fireEvent.change(await screen.findByLabelText('X axis (rows)'), { target: { value: '__days__' } });
+    await waitFor(() => expect(screen.getByText(/2 rows/i)).toBeInTheDocument());
     fireEvent.click(screen.getByText('Export CSV'));
     const text = await readBlobText(dl.getBlob());
-    expect(text).not.toMatch(/^Group,/m);
+    expect(text).toBe('Data,Total attempts\n\n# Days Reach,Alpha,Beta\n1,5,9\n2,7,');
+    await dl.restore();
+  });
+
+  it('a valid group field adds a Group row and clusters subjects', async () => {
+    const dl = mockDownload();
+    renderModal({ groupField: 'grp' });
+    await screen.findByLabelText('X axis (rows)');
+    await waitFor(() => expect(screen.getByText(/2 rows/i)).toBeInTheDocument());
+    fireEvent.click(screen.getByText('Export CSV'));
+    const text = await readBlobText(dl.getBlob());
+    expect(text).toMatch(/^Group,Control,Drug$/m);
     await dl.restore();
   });
 });