diff --git a/autotest/pst_from_tests.py b/autotest/pst_from_tests.py
index 7d60e608..6529937d 100644
--- a/autotest/pst_from_tests.py
+++ b/autotest/pst_from_tests.py
@@ -4603,13 +4603,16 @@ def test_vertex_grid(tmp_path):
         df_pp = pf.add_parameters(f,
                             zone_array=ib[layer],
                             par_type="pilotpoints",
-                            use_pp_zones=True,
+                            #use_pp_zones=True,
                             geostruct=grid_gs,
                             par_name_base=f.split('.')[1].replace("_","")+"pp",
                             pargp=f.split('.')[1].replace("_","")+"pp",
                             lower_bound=0.2,upper_bound=5.0,
                             ult_ubound=100, ult_lbound=0.01,
-                            pp_space=500) # `
+                            pp_options={"prep_hyperpars":False,
+                                        "pp_space":500,
+                                        "try_use_ppu":False,
+                                        "pp_zones":True}) # `
 
     tag = "sfr_packagedata"
     files = [f for f in os.listdir(template_ws) if tag in f.lower() and f.endswith(".txt")]
@@ -4681,9 +4684,14 @@ def test_vertex_grid(tmp_path):
         k = int(f.split('_layer')[-1].split('.')[0]) - 1
         a = np.loadtxt(os.path.join(template_ws, f))
         a_org = np.loadtxt(os.path.join(template_ws,'org', f))
+        assert a.shape == a_org.shape, (a.shape, a_org.shape)
+        assert np.isclose(a, a_org).all(), a-a_org
         # weak check
-        for zone in npfpar.loc[npfpar.pname.str.contains(f'layer{k+1}')].zone.unique():
-            assert np.isclose(abs((a/a_org)[ib[k]==int(zone)]-int(zone)).max(), 0)
+        zones = npfpar.loc[npfpar.pname.str.contains(f'layer{k+1}')].zone.unique()
+        # check all of zones are in ib[k]
+        assert set(zones).issubset(set(np.unique(ib[k]))), f"not all zones in ib for {f}"
+        for zone in zones:
+            assert np.isclose(abs((a/a_org)[ib[k]==int(zone)]-1).max(), 0), f"{f} zone {zone} failed check"
     return
 
 def test_defaults(tmp_path):
diff --git a/pyemu/utils/pp_utils.py b/pyemu/utils/pp_utils.py
index eaefc9bb..e9593e62 100644
--- a/pyemu/utils/pp_utils.py
+++ b/pyemu/utils/pp_utils.py
@@ -783,6 +783,10 @@ def prep_pp_hyperpars(file_tag,pp_filename,pp_info,out_filename,grid_dict,
     aniso_filename = file_tag + ".aniso.dat"
     zone_filename = file_tag + ".zone.dat"
 
+    if len(arr_shape) == 1 and type(arr_shape) is tuple:
+        arr_shape = (1,arr_shape[0])
+
+
     nodes = list(grid_dict.keys())
     nodes.sort()
     with open(os.path.join(ws,gridinfo_filename), 'w') as f:
@@ -798,7 +802,7 @@ def prep_pp_hyperpars(file_tag,pp_filename,pp_info,out_filename,grid_dict,
     np.savetxt(os.path.join(ws,aniso_filename), aniso, fmt="%20.8E")
 
     if zone_array is None:
-        zone_array = np.ones(shape,dtype=int)
+        zone_array = np.ones(arr_shape,dtype=int)
     np.savetxt(os.path.join(ws,zone_filename),zone_array,fmt="%5d")
 
 
diff --git a/pyemu/utils/pst_from.py b/pyemu/utils/pst_from.py
index 5a921489..ed07b512 100644
--- a/pyemu/utils/pst_from.py
+++ b/pyemu/utils/pst_from.py
@@ -2118,8 +2118,21 @@ def add_parameters(
                 and zone_array is not None
                 and len(zone_array.shape) == 1
         )
+        checker2 = (
+                self._spatial_reference is not None
+                and not isinstance(self._spatial_reference, dict)
+                and self._spatial_reference.grid_type == 'vertex'
+                and zone_array is not None
+                and len(zone_array.shape) == 2
+                and zone_array.shape[0] == 1
+                and zone_array.shape[1] > 1
+        )
         if checker:
             zone_array = np.reshape(zone_array, (zone_array.shape[0], 1))
+        # when accesing ib for a 1layer model, the returned array has shape (1,ncpl)
+        if checker2:
+            zone_array = np.reshape(zone_array, (zone_array.shape[1], 1))
+
 
         # Get useful variables from arguments passed
         # if index_cols passed as a dictionary that maps i,j information
@@ -2452,7 +2465,7 @@ def add_parameters(
                         orgdata = ar.shape
                         for i, chk in checkref.items():
                             assert orgdata[i] == chk[1], (
-                                f"Spatial reference {chk[0]} not equal to original data {chk[0]} for\n"
+                                f"Spatial reference {chk[1]} not equal to original data {orgdata[i]} for\n"
                                 + os.path.join(
                                     *os.path.split(self.original_file_d)[1:], mod_file
                                 )