diff --git a/setup.py b/setup.py
index 7e8d917..9b226ed 100644
--- a/setup.py
+++ b/setup.py
@@ -28,4 +28,6 @@
 )
 # TODO: the EPSG:<horiz>+<vert> format is not supported in rio 1.3.3, gdal 3.5.3, proj 9.1.0, but is supported
 #  in rio 1.3.6, gdal 3.6.2, proj 9.1.1.  The exact version where support begins (proj=9.1.1?) should be set in
-#  setup.py.  Then the multithreaded overview building bug should be fixed in gdal 3.8.
+#  setup.py (note that pyproj seems to support the EPSG:<>+<> format with PROJ<9.1.1 so something is exactly right
+#  with thre prev statement).  Then the multithreaded overview building bug should be fixed in gdal 3.8.  Also note
+#  that proj<9.1.0 auto promotes 2d CRSs to 3d.
diff --git a/tests/test_io.py b/tests/test_io.py
index 4a941a1..8c52c0e 100644
--- a/tests/test_io.py
+++ b/tests/test_io.py
@@ -214,7 +214,7 @@ def test_rio_transform_vdatum_both(src_crs: str, dst_crs: str, request: pytest.F
     ('utm34n_crs', 'wgs84_egm96_crs'),
     ('utm34n_crs', 'wgs84_egm2008_crs'),
 ])  # yapf: disable
-def _test_rio_transform_vdatum_one(src_crs: str, dst_crs: str, request: pytest.FixtureRequest):
+def test_rio_transform_vdatum_one(src_crs: str, dst_crs: str, request: pytest.FixtureRequest):
     """
     Test rasterio.warp.transform does not adjust the z coordinate with one of the source and destination CRS vertical
     datums specified.
@@ -222,10 +222,9 @@ def _test_rio_transform_vdatum_one(src_crs: str, dst_crs: str, request: pytest.F
     src_crs: rio.CRS = rio.CRS.from_string(request.getfixturevalue(src_crs))
     dst_crs: rio.CRS = rio.CRS.from_string(request.getfixturevalue(dst_crs))
     src_xyz = [[10.], [10.], [100.]]
-    import os
-    os.environ.update(ALLOW_ELLIPSOIDAL_HEIGHT_AS_VERTICAL_CRS='YES')
-    with rio.Env(ALLOW_ELLIPSOIDAL_HEIGHT_AS_VERTICAL_CRS='YES'):
-        dst_xyz = transform(src_crs, dst_crs, *src_xyz)
+    dst_xyz = transform(src_crs, dst_crs, *src_xyz)
+    if rio.get_proj_version() >= (9, 1, 1):
+        # prior proj versions promote 2D->3D with ellipsoidal height
         assert dst_xyz[2][0] == pytest.approx(src_xyz[2][0], abs=1e-6)
 
 
diff --git a/tests/test_ortho.py b/tests/test_ortho.py
index 31fac00..f56e923 100644
--- a/tests/test_ortho.py
+++ b/tests/test_ortho.py
@@ -209,7 +209,7 @@ def test_reproject_dem_vdatum_both(
         ('float_utm34n_egm96_dem_file', 'utm34n_crs'),
     ],
 )  # yapf: disable  # @formatter:on
-def _test_reproject_dem_vdatum_one(
+def test_reproject_dem_vdatum_one(
     rgb_byte_src_file: Path, dem_file: str, pinhole_camera: Camera, crs: str, request: pytest.FixtureRequest
 ):
     """ Test DEM reprojection does no altitude adjustment when one of DEM and ortho vertical datums are specified. """
@@ -234,7 +234,9 @@ def _test_reproject_dem_vdatum_one(
     assert test_array.shape == ortho._dem_array.shape
 
     mask = ~np.isnan(test_array) & ~np.isnan(ortho._dem_array)
-    assert test_array[mask] == pytest.approx(ortho._dem_array[mask], abs=1e-3)
+    if rio.get_proj_version() >= (9, 1, 0):
+        # prior proj versions promote 2D->3D with ellipsoidal height
+        assert test_array[mask] == pytest.approx(ortho._dem_array[mask], abs=1e-3)
 
 
 @pytest.mark.parametrize('num_pts', [40, 100, 400, 1000, 4000])
@@ -316,8 +318,9 @@ def test_mask_dem(
     assert dem_transform_mask == dem_transform
     assert dem_mask.shape == ortho_mask.shape
     assert dem_mask[ortho_mask].sum() / ortho_mask.sum() > 0.95
-    cc = np.corrcoef(dem_mask.flatten(), ortho_mask.flatten())
-    assert (np.all(dem_mask) and np.all(ortho_mask)) or (cc[0, 1] > 0.9)
+    if not np.all(dem_mask) and np.all(ortho_mask):
+        cc = np.corrcoef(dem_mask.flatten(), ortho_mask.flatten())
+        assert cc[0, 1] > 0.9
 
     if False:
         # debug plotting code