diff --git a/app/broadcast_areas/models.py b/app/broadcast_areas/models.py
index 105a456dc..d7776c4ed 100644
--- a/app/broadcast_areas/models.py
+++ b/app/broadcast_areas/models.py
@@ -163,10 +163,11 @@ class CustomBroadcastArea(BaseBroadcastArea):
     simple_polygons = polygons
 
     @cached_property
-    def overlapping_areas(self):
+    def nearby_electoral_wards(self):
         if not self.polygons:
             return []
         return broadcast_area_libraries.get_areas_with_simple_polygons([
+            # We only index electoral wards in the RTree
             overlap.data for overlap in rtree_index.query(
                 Rect(*self.polygons.bounds)
             )
@@ -176,7 +177,7 @@ class CustomBroadcastArea(BaseBroadcastArea):
     def count_of_phones(self):
         return sum(
             area.simple_polygons.ratio_of_intersection_with(self.polygons) * area.count_of_phones
-            for area in self.overlapping_areas
+            for area in self.nearby_electoral_wards
         )
 
 
diff --git a/tests/app/broadcast_areas/test_broadcast_area.py b/tests/app/broadcast_areas/test_broadcast_area.py
index 4c2af384b..ef862f10d 100644
--- a/tests/app/broadcast_areas/test_broadcast_area.py
+++ b/tests/app/broadcast_areas/test_broadcast_area.py
@@ -386,7 +386,7 @@ def test_count_of_phones_for_custom_area(
     )
 
     assert sorted(
-        overlap.name for overlap in area.overlapping_areas
+        overlap.name for overlap in area.nearby_electoral_wards
     ) == expected_possible_overlaps
 
     assert close_enough(area.count_of_phones, expected_count_of_phones)