diff --git a/backend/app/services/vector_feature_service.py b/backend/app/services/vector_feature_service.py
index 9c54717b..a731926e 100644
--- a/backend/app/services/vector_feature_service.py
+++ b/backend/app/services/vector_feature_service.py
@@ -11,7 +11,7 @@ from geoalchemy2.shape import to_shape
 from shapely.geometry import box, mapping, shape
 from shapely.ops import transform as transform_geometry
 from shapely.validation import make_valid
-from sqlalchemy import Float, String, cast, func
+from sqlalchemy import Float, String, case, cast, func
 
 from app.core.errors import AppError
 from app.models import Dataset, VectorFeature
@@ -778,12 +778,18 @@ class VectorFeatureService:
             )
 
         if method == "intersection_area":
-            measured_geometry = (
-                VectorFeature.geometry
-                if full_dataset_area
-                else func.ST_Intersection(VectorFeature.geometry, selection_shape)
-            )
-            area_expression = func.ST_Area(func.ST_Transform(measured_geometry, 31370))
+            source_area = func.ST_Area(func.ST_Transform(VectorFeature.geometry, 31370))
+            if full_dataset_area:
+                area_expression = source_area
+            else:
+                covered_by_selection = func.ST_CoveredBy(VectorFeature.geometry, selection_shape)
+                intersection_area = func.ST_Area(
+                    func.ST_Transform(func.ST_Intersection(VectorFeature.geometry, selection_shape), 31370)
+                )
+                area_expression = case(
+                    (covered_by_selection, source_area),
+                    else_=intersection_area,
+                )
             area_m2 = db.query(func.coalesce(func.sum(area_expression), 0.0)).filter(*metric_filter).scalar()
             divisor = 10_000.0 if unit == "ha" else 1.0
             metric_value = float(area_m2 or 0.0) / divisor
@@ -808,12 +814,17 @@ class VectorFeatureService:
                 )
             numeric_value = cast(VectorFeature.properties_json.op("->>")(property_name), Float)
             value_expression = numeric_value
+            covered_by_selection = None
             if method == "area_weighted_sum" and not full_dataset_area:
                 source_area = func.ST_Area(func.ST_Transform(VectorFeature.geometry, 31370))
                 intersection_area = func.ST_Area(
                     func.ST_Transform(func.ST_Intersection(VectorFeature.geometry, selection_shape), 31370)
                 )
-                coverage_ratio = intersection_area / func.nullif(source_area, 0.0)
+                covered_by_selection = func.ST_CoveredBy(VectorFeature.geometry, selection_shape)
+                coverage_ratio = case(
+                    (covered_by_selection, 1.0),
+                    else_=intersection_area / func.nullif(source_area, 0.0),
+                )
                 value_expression = numeric_value * coverage_ratio
             aggregate_function = {
                 "mean": func.avg,
@@ -831,7 +842,7 @@ class VectorFeatureService:
                 partial_feature_count = (
                     db.query(func.count(VectorFeature.id))
                     .filter(*metric_filter)
-                    .filter(coverage_ratio < 0.999999)
+                    .filter(~covered_by_selection)
                     .scalar()
                 )
                 is_estimate = bool(config.get("is_estimate", False)) or bool(partial_feature_count)