diff --git a/config/dot/quickshell/modules/bar/ActivityPanel.qml b/config/dot/quickshell/modules/bar/ActivityPanel.qml
index e84b4fc..eb71faf 100644
--- a/config/dot/quickshell/modules/bar/ActivityPanel.qml
+++ b/config/dot/quickshell/modules/bar/ActivityPanel.qml
@@ -15,7 +15,11 @@ PanelWindow {
     color: "transparent"
     anchors.top: true
     anchors.right: true
-    margins.top: Theme.barHeight + Theme.barGap * 2
+    // The gap ALONE, not the bar height plus the gap. exclusiveZone 0 means
+    // "reserve nothing, but respect what others reserved", so this surface
+    // already begins below the bar's zone -- adding the bar height here counted
+    // it twice and left the surface floating 48px under the bar instead of 12.
+    margins.top: Theme.barGap * 2
     margins.right: Theme.barSideMargin
     exclusiveZone: 0
     implicitWidth: 350
diff --git a/config/dot/quickshell/modules/clipboard/ClipboardPanel.qml b/config/dot/quickshell/modules/clipboard/ClipboardPanel.qml
index 298ae7d..bcf9008 100644
--- a/config/dot/quickshell/modules/clipboard/ClipboardPanel.qml
+++ b/config/dot/quickshell/modules/clipboard/ClipboardPanel.qml
@@ -20,8 +20,11 @@ PanelWindow {
         top: true
         right: true
     }
+    // The gap ALONE, not the bar height plus the gap -- see the note in
+    // QuickSettings.qml: exclusiveZone 0 already places this below the bar's
+    // reserved zone, so adding the bar height counted it twice.
     margins {
-        top: Theme.barHeight + Theme.barGap * 2
+        top: Theme.barGap * 2
         right: Theme.barSideMargin
     }
 
diff --git a/config/dot/quickshell/modules/datemenu/DateMenu.qml b/config/dot/quickshell/modules/datemenu/DateMenu.qml
index 8ee8030..84ad5a8 100644
--- a/config/dot/quickshell/modules/datemenu/DateMenu.qml
+++ b/config/dot/quickshell/modules/datemenu/DateMenu.qml
@@ -28,7 +28,11 @@ PanelWindow {
     color: "transparent"
 
     anchors.top: true
-    margins.top: Theme.barHeight + Theme.barGap * 2
+    // The gap ALONE, not the bar height plus the gap. exclusiveZone 0 means
+    // "reserve nothing, but respect what others reserved", so this surface
+    // already begins below the bar's zone -- adding the bar height here counted
+    // it twice and left the surface floating 48px under the bar instead of 12.
+    margins.top: Theme.barGap * 2
     exclusiveZone: 0
 
     implicitWidth: 760
diff --git a/config/dot/quickshell/modules/notifications/Toasts.qml b/config/dot/quickshell/modules/notifications/Toasts.qml
index f45ef57..8b93353 100644
--- a/config/dot/quickshell/modules/notifications/Toasts.qml
+++ b/config/dot/quickshell/modules/notifications/Toasts.qml
@@ -17,7 +17,11 @@ PanelWindow {
 
     anchors.top: true
     anchors.right: true
-    margins.top: Theme.barHeight + Theme.barGap * 2
+    // The gap ALONE, not the bar height plus the gap. exclusiveZone 0 means
+    // "reserve nothing, but respect what others reserved", so this surface
+    // already begins below the bar's zone -- adding the bar height here counted
+    // it twice and left the surface floating 48px under the bar instead of 12.
+    margins.top: Theme.barGap * 2
     margins.right: Theme.barSideMargin
     exclusiveZone: 0
 
diff --git a/config/dot/quickshell/modules/signals/SignalGlass.qml b/config/dot/quickshell/modules/signals/SignalGlass.qml
index 25537b7..121fea9 100644
--- a/config/dot/quickshell/modules/signals/SignalGlass.qml
+++ b/config/dot/quickshell/modules/signals/SignalGlass.qml
@@ -22,7 +22,11 @@ PanelWindow {
 
     screen: root.modelData
     anchors.top: true
-    margins.top: Theme.barHeight + Theme.barGap * 2
+    // The gap ALONE, not the bar height plus the gap. exclusiveZone 0 means
+    // "reserve nothing, but respect what others reserved", so this surface
+    // already begins below the bar's zone -- adding the bar height here counted
+    // it twice and left the surface floating 48px under the bar instead of 12.
+    margins.top: Theme.barGap * 2
     exclusiveZone: 0
     implicitWidth: root.showingEvent ? 388 : 438
     implicitHeight: root.showingEvent ? 76 : 132
diff --git a/tests/quickshell/layer-margin-contract.sh b/tests/quickshell/layer-margin-contract.sh
new file mode 100755
index 0000000..cacea3d
--- /dev/null
+++ b/tests/quickshell/layer-margin-contract.sh
@@ -0,0 +1,74 @@
+#!/usr/bin/env bash
+
+# A surface that respects the bar's reserved space must not also subtract it by
+# hand.
+#
+# wlr-layer-shell has three behaviors and only the middle one is subtle:
+#
+#   exclusiveZone > 0   reserve this much space; other surfaces are pushed out
+#   exclusiveZone = 0   reserve nothing, but RESPECT what others reserved
+#   exclusiveZone < 0   reserve nothing and ignore what others reserved
+#
+# Every popover here uses 0, so the compositor has already placed it below the
+# bar before its own margin applies. Adding Theme.barHeight to that margin
+# counts the bar twice. That is not a crash and not a warning -- the panel
+# simply opens lower than intended, which is how the control center spent its
+# life hanging 38px under a bar it was written to sit 2px below, and five other
+# surfaces sat at 48px instead of 12px.
+#
+# The rule is mechanical, so a test can hold it: with exclusiveZone 0, a margin
+# is the GAP, never the gap plus what someone else reserved.
+#
+# Static and read-only.
+
+set -uo pipefail
+
+repo_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+modules="$repo_dir/config/dot/quickshell/modules"
+
+fail() {
+    printf 'layer margin contract: %s\n' "$1" >&2
+    exit 1
+}
+
+[[ -d "$modules" ]] || fail 'the modules directory is missing'
+
+# The premise: the bar is what reserves space at the top. If that ever changes,
+# the rule below stops being the right rule and this should be revisited rather
+# than kept passing.
+bar="$modules/bar/Bar.qml"
+[[ -r "$bar" ]] || fail 'Bar.qml is missing'
+grep -q 'exclusiveZone: Theme.barHeight' "$bar" \
+    || fail 'the bar no longer reserves its own height, so what popovers should offset by has changed'
+
+violations=""
+checked=0
+
+while read -r file; do
+    [[ -n "$file" ]] || continue
+    grep -q 'PanelWindow' "$file" || continue
+
+    # Only surfaces that respect other zones. A surface with a negative zone is
+    # positioned from the screen edge and SHOULD carry the bar height itself.
+    zone="$(grep -oE 'exclusiveZone:[[:space:]]*-?[0-9]+' "$file" | head -1 | grep -oE '\-?[0-9]+$')"
+    [[ "$zone" == "0" ]] || continue
+    checked=$((checked + 1))
+
+    # Margins only. Theme.barHeight is legitimate elsewhere -- sizing a row to
+    # match the bar, for instance -- so this looks at the placement lines.
+    offenders="$(grep -nE '^[[:space:]]*(margins\.(top|bottom)|top|bottom):.*Theme\.barHeight' "$file" || true)"
+    if [[ -n "$offenders" ]]; then
+        while IFS= read -r line; do
+            violations+="    ${file#$repo_dir/}:${line}"$'\n'
+        done <<<"$offenders"
+    fi
+done < <(find "$modules" -name '*.qml' | sort)
+
+(( checked > 0 )) || fail 'no surfaces with exclusiveZone 0 were found, so this checked nothing'
+
+if [[ -n "$violations" ]]; then
+    printf 'layer margin contract: these surfaces respect the bar'"'"'s reserved space AND add it to their margin, so they open one bar-height too low:\n%s' "$violations" >&2
+    exit 1
+fi
+
+printf 'layer margin contract: PASS (%d surfaces respect the bar without double-counting it)\n' "$checked"