diff --git a/ax/modelbridge/tests/test_registry.py b/ax/modelbridge/tests/test_registry.py
index 568e6d04335..0a3c7547f25 100644
--- a/ax/modelbridge/tests/test_registry.py
+++ b/ax/modelbridge/tests/test_registry.py
@@ -47,9 +47,10 @@
 from botorch.models.multitask import MultiTaskGP
 from botorch.utils.types import DEFAULT
 from gpytorch.kernels.matern_kernel import MaternKernel
+from gpytorch.kernels.rbf_kernel import RBFKernel
 from gpytorch.kernels.scale_kernel import ScaleKernel
 from gpytorch.mlls.exact_marginal_log_likelihood import ExactMarginalLogLikelihood
-from gpytorch.priors.torch_priors import GammaPrior
+from gpytorch.priors.torch_priors import GammaPrior, LogNormalPrior
 
 
 class ModelRegistryTest(TestCase):
@@ -452,12 +453,7 @@ def test_ST_MTGP(self, use_saas: bool = False) -> None:
                 ]
             )
 
-            lengthscale_priors = [
-                GammaPrior(6.0, 3.0),
-                GammaPrior(3.0, 6.0),
-            ]
-
-            for surrogate, lengthscale_prior in zip(surrogates, lengthscale_priors):
+            for surrogate, default_model in zip(surrogates, (False, True)):
                 constructor = Models.SAAS_MTGP if use_saas else Models.ST_MTGP
                 mtgp = constructor(
                     experiment=exp,
@@ -468,26 +464,25 @@ def test_ST_MTGP(self, use_saas: bool = False) -> None:
                 self.assertIsInstance(mtgp, TorchModelBridge)
                 self.assertIsInstance(mtgp.model, BoTorchModel)
                 self.assertEqual(mtgp.model.acquisition_class, Acquisition)
-
                 self.assertIsInstance(mtgp.model.surrogate.model, ModelListGP)
-                models = mtgp.model.surrogate.model.models
 
-                for i in range(len(models)):
+                for model in mtgp.model.surrogate.model.models:
                     self.assertIsInstance(
-                        models[i],
+                        model,
                         SaasFullyBayesianMultiTaskGP if use_saas else MultiTaskGP,
                     )
-                    if use_saas is False:
-                        self.assertIsInstance(models[i].covar_module, ScaleKernel)
-                        base_kernel = models[i].covar_module.base_kernel
+                    if use_saas is False and default_model is False:
+                        self.assertIsInstance(model.covar_module, ScaleKernel)
+                        base_kernel = model.covar_module.base_kernel
                         self.assertIsInstance(base_kernel, MaternKernel)
                         self.assertEqual(
-                            base_kernel.lengthscale_prior.concentration,
-                            lengthscale_prior.concentration,
+                            base_kernel.lengthscale_prior.concentration, 6.0
                         )
-                        self.assertEqual(
-                            base_kernel.lengthscale_prior.rate,
-                            lengthscale_prior.rate,
+                        self.assertEqual(base_kernel.lengthscale_prior.rate, 3.0)
+                    elif use_saas is False:
+                        self.assertIsInstance(model.covar_module, RBFKernel)
+                        self.assertIsInstance(
+                            model.covar_module.lengthscale_prior, LogNormalPrior
                         )
 
                 gr = mtgp.gen(