Increase the limit for PP instead of M2L or M2P to a VEC_SIZE

src/cell.c

@@ -6393,8 +6393,8 @@ int cell_can_use_pair_mm(const struct cell *ci, const struct cell *cj,
   const double dim[3] = {s->dim[0], s->dim[1], s->dim[2]};
 
   /* Check for trivial cases */
-  if (ci->grav.count < 2) return 0;
-  if (cj->grav.count < 2) return 0;
+  if (ci->grav.count < VEC_SIZE) return 0;
+  if (cj->grav.count < VEC_SIZE) return 0;
 
   /* Recover the multipole information */
   const struct gravity_tensors *const multi_i = ci->grav.multipole;

src/runner_doiact_grav.c

@@ -1011,8 +1011,8 @@ void runner_dopair_grav_pp(struct runner *r, struct cell *ci, struct cell *cj,
           gcount_j);
 #endif
 
-  const int allow_multipole_i = allow_mpole && ci->grav.count > 1;
-  const int allow_multipole_j = allow_mpole && cj->grav.count > 1;
+  const int allow_multipole_i = allow_mpole && ci->grav.count > VEC_SIZE;
+  const int allow_multipole_j = allow_mpole && cj->grav.count > VEC_SIZE;
 
   /* Fill the caches */
   gravity_cache_populate(e->max_active_bin, allow_multipole_j, periodic, dim,
@@ -1960,7 +1960,7 @@ void runner_dopair_recursive_grav(struct runner *r, struct cell *ci,
   /* OK, we actually need to compute this pair. Let's find the cheapest
    * option... */
 
-  if (ci->grav.count < 2 || cj->grav.count < 2) {
+  if (ci->grav.count < VEC_SIZE || cj->grav.count < VEC_SIZE) {
 
     /* We have two cheap cells. Go P-P. */
     runner_dopair_grav_pp_no_cache(r, ci, cj, /*symmetric=*/1);