diff --git a/src/db/db/dbHierProcessor.cc b/src/db/db/dbHierProcessor.cc
index 6d7253eb7..d1008dbfd 100644
--- a/src/db/db/dbHierProcessor.cc
+++ b/src/db/db/dbHierProcessor.cc
@@ -1900,7 +1900,7 @@ template <class TS, class TI>
 struct scan_shape2shape_same_layer_flat
 {
   void
-  operator () (const generic_shape_iterator<TS> &, unsigned int, shape_interactions<TS, TI> &, db::Coord) const
+  operator () (const generic_shape_iterator<TS> &, bool, unsigned int, shape_interactions<TS, TI> &, db::Coord) const
   {
     //  cannot have different types on the same layer
     tl_assert (false);
@@ -1911,7 +1911,7 @@ template <class T>
 struct scan_shape2shape_same_layer_flat<T, T>
 {
   void
-  operator () (const generic_shape_iterator<T> &subjects, unsigned int intruder_layer, shape_interactions<T, T> &interactions, db::Coord dist) const
+  operator () (const generic_shape_iterator<T> &subjects, bool needs_isolated_subjects, unsigned int intruder_layer, shape_interactions<T, T> &interactions, db::Coord dist) const
   {
     db::box_scanner<T, int> scanner;
     interaction_registration_shape1<T, T> rec (&interactions, intruder_layer);
@@ -1924,6 +1924,11 @@ struct scan_shape2shape_same_layer_flat<T, T>
       const T *shape = is.operator-> ();
       scanner.insert (shape, id);
 
+      //  create subject for subject vs. nothing interactions
+      if (needs_isolated_subjects) {
+        interactions.add_subject (id, *shape);
+      }
+
     }
 
     scanner.process (rec, dist, db::box_convert<T> ());
@@ -1949,7 +1954,7 @@ template <class TS, class TI>
 struct scan_shape2shape_different_layers_flat
 {
   void
-  operator () (const generic_shape_iterator<TS> &subjects, const generic_shape_iterator<TI> &intruders, unsigned int intruder_layer, shape_interactions<TS, TI> &interactions, db::Coord dist) const
+  operator () (const generic_shape_iterator<TS> &subjects, const generic_shape_iterator<TI> &intruders, bool needs_isolated_subjects, unsigned int intruder_layer, shape_interactions<TS, TI> &interactions, db::Coord dist) const
   {
     db::box_scanner2<TS, int, TI, int> scanner;
     interaction_registration_shape2shape<TS, TI> rec (0 /*layout*/, &interactions, intruder_layer);
@@ -1966,14 +1971,46 @@ struct scan_shape2shape_different_layers_flat
 
     db::Box common_box = intruders_box & subjects_box;
     if (common_box.empty ()) {
+
+      if (needs_isolated_subjects) {
+        for (generic_shape_iterator<TS> is = subjects; ! is.at_end (); ++is) {
+          //  create subject for subject vs. nothing interactions
+          interactions.add_subject (interactions.next_id (), *is);
+        }
+      }
+
       return;
+
     }
 
     addressable_shape_delivery<TS> is;
 
-    is = addressable_shape_delivery<TS> (subjects.confined (common_box, true));
-    for ( ; !is.at_end (); ++is) {
-      scanner.insert1 (is.operator-> (), interactions.next_id ());
+    if (needs_isolated_subjects) {
+
+      box_convert<TS> bcs;
+
+      is = addressable_shape_delivery<TS> (subjects);
+      for ( ; !is.at_end (); ++is) {
+
+        unsigned int id = interactions.next_id ();
+        const TS *shape = is.operator-> ();
+
+        if (bcs (*shape).overlaps (common_box)) {
+          scanner.insert1 (shape, id);
+        }
+
+        //  create subject for subject vs. nothing interactions
+        interactions.add_subject (id, *shape);
+
+      }
+
+    } else {
+
+      is = addressable_shape_delivery<TS> (subjects.confined (common_box, true));
+      for ( ; !is.at_end (); ++is) {
+        scanner.insert1 (is.operator-> (), interactions.next_id ());
+      }
+
     }
 
     addressable_shape_delivery<TI> ii (intruders.confined (common_box, true));
@@ -2001,15 +2038,16 @@ local_processor<TS, TI, TR>::run_flat (const generic_shape_iterator<TS> &subject
 
   shape_interactions<TS, TI> interactions;
 
-  if (op->on_empty_intruder_hint () != OnEmptyIntruderHint::Drop) {
+  bool needs_isolated_subjects = (op->on_empty_intruder_hint () != OnEmptyIntruderHint::Drop);
+  if (intruders.empty () && needs_isolated_subjects) {
     add_subjects_vs_nothing_flat<TS, TI> () (subjects, interactions);
   }
 
   for (typename std::vector<generic_shape_iterator<TI> >::const_iterator il = intruders.begin (); il != intruders.end (); ++il) {
     if (*il == subjects) {
-      scan_shape2shape_same_layer_flat<TS, TI> () (subjects, (unsigned int) (il - intruders.begin ()), interactions, op->dist ());
+      scan_shape2shape_same_layer_flat<TS, TI> () (subjects, needs_isolated_subjects, (unsigned int) (il - intruders.begin ()), interactions, op->dist ());
     } else {
-      scan_shape2shape_different_layers_flat<TS, TI> () (subjects, *il, (unsigned int) (il - intruders.begin ()), interactions, op->dist ());
+      scan_shape2shape_different_layers_flat<TS, TI> () (subjects, *il, needs_isolated_subjects, (unsigned int) (il - intruders.begin ()), interactions, op->dist ());
     }
   }