diff --git a/scripts/sitediagrams.py b/scripts/sitediagrams.py
index 1d8b51835..f73cbe581 100644
--- a/scripts/sitediagrams.py
+++ b/scripts/sitediagrams.py
@@ -226,8 +226,9 @@ def flow(boxes: list[Box], vertical: bool, total: float) -> tuple[float, float,
     if vertical:
         width = total
         y = 1.0
-        for index, box in enumerate(boxes):
-            title_lines, body, height = _box_height(box, width - 2)
+        measured = [_box_height(box, width - 2) for box in boxes]
+        height = max(m[2] for m in measured)
+        for index, (box, (title_lines, body, _)) in enumerate(zip(boxes, measured)):
             out.extend(_draw_box(box, 1, y, width - 2, height, title_lines, body))
             y += height
             if index < len(boxes) - 1:
@@ -238,10 +239,11 @@ def flow(boxes: list[Box], vertical: bool, total: float) -> tuple[float, float,
     width = (total - gap * (len(boxes) - 1) - 2) / len(boxes)
     measured = [_box_height(box, width) for box in boxes]
     height = max(m[2] for m in measured)
-    for index, (box, (title_lines, body, own)) in enumerate(zip(boxes, measured)):
+    for index, (box, (title_lines, body, _)) in enumerate(zip(boxes, measured)):
         x = 1 + index * (width + gap)
-        # A box is as tall as its lines, centred on the row the arrows run along.
-        out.extend(_draw_box(box, x, 1 + (height - own) / 2, width, own, title_lines, body))
+        # One height for the row: boxes as tall as their own lines made four
+        # sizes side by side.
+        out.extend(_draw_box(box, x, 1, width, height, title_lines, body))
         if index < len(boxes) - 1:
             mid = 1 + height / 2
             out.extend(_line([(x + width, mid), (x + width + gap - 1, mid)]))
@@ -253,8 +255,9 @@ def columns(boxes: list[Box], vertical: bool, total: float) -> tuple[float, floa
     out: list[str] = []
     if vertical:
         y = 1.0
-        for box in boxes:
-            title_lines, body, height = _box_height(box, total - 2)
+        measured = [_box_height(box, total - 2) for box in boxes]
+        height = max(m[2] for m in measured)
+        for box, (title_lines, body, _) in zip(boxes, measured):
             out.extend(_draw_box(box, 1, y, total - 2, height, title_lines, body))
             y += height + 12
         return total, y - 11, out
@@ -262,8 +265,8 @@ def columns(boxes: list[Box], vertical: bool, total: float) -> tuple[float, floa
     width = (total - gap * (len(boxes) - 1) - 2) / len(boxes)
     measured = [_box_height(box, width) for box in boxes]
     height = max(m[2] for m in measured)
-    for index, (box, (title_lines, body, own)) in enumerate(zip(boxes, measured)):
-        out.extend(_draw_box(box, 1 + index * (width + gap), 1, width, own, title_lines, body))
+    for index, (box, (title_lines, body, _)) in enumerate(zip(boxes, measured)):
+        out.extend(_draw_box(box, 1 + index * (width + gap), 1, width, height, title_lines, body))
     return total, height + 2, out
 
 
diff --git a/tests/test_site_r2_wiki.py b/tests/test_site_r2_wiki.py
index 2c85a1f76..e2efe200e 100644
--- a/tests/test_site_r2_wiki.py
+++ b/tests/test_site_r2_wiki.py
@@ -328,10 +328,14 @@ class DiagramText(unittest.TestCase):
         html = sitediagrams.figure_html("bios-chain")
         self.assertRegex(html, r'<text [^>]*style="font-family: var\(--sl-font-mono[^>]*>/userdata/bios/</text>')
 
-    def test_boxes_take_the_height_of_their_lines(self):
-        width, _height, body = sitediagrams.flow(sitediagrams._bios_chain_boxes(), False, sitediagrams.WIDE)
-        heights = {float(h) for h in re.findall(r'<rect [^>]*height="([\d.]+)"[^>]*class="rb-d-box', "".join(body))}
-        self.assertGreater(len(heights), 1)
+    def test_boxes_of_a_row_share_one_height(self):
+        for layout in (sitediagrams.flow, sitediagrams.columns):
+            for vertical, total in ((False, sitediagrams.WIDE), (True, sitediagrams.NARROW)):
+                _width, _height, body = layout(sitediagrams._bios_chain_boxes(), vertical, total)
+                heights = {float(h) for h in re.findall(r'<rect [^>]*height="([\d.]+)"[^>]*class="rb-d-box',
+                                                         "".join(body))}
+                with self.subTest(layout=layout.__name__, vertical=vertical):
+                    self.assertEqual(len(heights), 1)
 
 
 class ExampleHashesStayOutOfSearch(unittest.TestCase):