diff --git a/src/hssm/distribution_utils/onnx/onnx.py b/src/hssm/distribution_utils/onnx/onnx.py
index 6bacfe07..6a9cc3b7 100644
--- a/src/hssm/distribution_utils/onnx/onnx.py
+++ b/src/hssm/distribution_utils/onnx/onnx.py
@@ -57,6 +57,7 @@ def make_jax_logp_funcs_from_onnx(
     )
 
     scalars_only = all(not is_reg for is_reg in params_is_reg)
+    print("scalars only: ", scalars_only)
 
     def logp(*inputs) -> jnp.ndarray:
         """Compute the log-likelihood.
@@ -76,11 +77,14 @@ def logp(*inputs) -> jnp.ndarray:
             The element-wise log-likelihoods.
         """
         # Makes a matrix to feed to the LAN model
+        print("scalars only: ", scalars_only)
+        print("params only: ", params_only)
         if params_only:
             input_vector = jnp.array(inputs)
         else:
             data = inputs[0]
             dist_params = inputs[1:]
+            print([inp.shape for inp in dist_params])
             param_vector = jnp.array([inp.squeeze() for inp in dist_params])
             if param_vector.shape[-1] == 1:
                 param_vector = param_vector.squeeze(axis=-1)
@@ -89,6 +93,7 @@ def logp(*inputs) -> jnp.ndarray:
         return interpret_onnx(loaded_model.graph, input_vector)[0].squeeze()
 
     if params_only and scalars_only:
+        print("passing scalars only case")
         logp_vec = lambda *inputs: logp(*inputs).reshape((1,))
         return jit(logp_vec), jit(grad(logp)), logp_vec
 
diff --git a/src/hssm/hssm.py b/src/hssm/hssm.py
index 13db4ea6..58294c3c 100644
--- a/src/hssm/hssm.py
+++ b/src/hssm/hssm.py
@@ -569,9 +569,11 @@ def sample(
                 )
 
         self._inference_obj = self.model.fit(
-            inference_method="mcmc"
-            if sampler in ["mcmc", "nuts_numpyro", "nuts_blackjax"]
-            else sampler,
+            inference_method=(
+                "mcmc"
+                if sampler in ["mcmc", "nuts_numpyro", "nuts_blackjax"]
+                else sampler
+            ),
             init=init,
             include_response_params=include_response_params,
             **kwargs,
@@ -1549,14 +1551,8 @@ def _get_deterministic_var_names(self, idata) -> list[str]:
             if param.is_regression
         ]
 
-        # Handle specific case where parent is not explictly in traces
-        if ("~" + self._parent in var_names) and (
-            self._parent not in idata.posterior.data_vars
-        ):
-            var_names.remove("~" + self._parent)
-
-        if f"{self.response_str}_mean" in idata["posterior"].data_vars:
-            var_names.append(f"~{self.response_str}_mean")
+        if f"{self._parent}_mean" in idata["posterior"].data_vars:
+            var_names.append(f"~{self._parent}_mean")
 
         return var_names
 
diff --git a/src/hssm/param.py b/src/hssm/param.py
index 931a7dac..07062e53 100644
--- a/src/hssm/param.py
+++ b/src/hssm/param.py
@@ -144,7 +144,10 @@ def override_default_priors(self, data: pd.DataFrame, eval_env: dict[str, Any]):
         """
         self._ensure_not_converted(context="prior")
 
-        if not self.is_regression:
+        # If no regression, or the parameter is the parent and does not have a
+        # formula attached (in which case it still gets a trial wise deterministic)
+        # do nothing
+        if not self.is_regression or (self.is_parent and self.formula is None):
             return
 
         override_priors = {}
@@ -213,7 +216,10 @@ def override_default_priors_ddm(self, data: pd.DataFrame, eval_env: dict[str, An
         self._ensure_not_converted(context="prior")
         assert self.name is not None
 
-        if not self.is_regression:
+        # If no regression, or the parameter is the parent and does not have a
+        # formula attached (in which case it still gets a trial wise deterministic)
+        # do nothing
+        if not self.is_regression or (self.is_parent and self.formula is None):
             return
 
         override_priors = {}
@@ -380,7 +386,7 @@ def is_regression(self) -> bool:
         bool
             A boolean that indicates if a regression is specified.
         """
-        return self.formula is not None
+        return self.formula is not None or self._is_parent
 
     @property
     def is_parent(self) -> bool:
diff --git a/tests/slow/test_mcmc.py b/tests/slow/test_mcmc.py
index 2ddc6274..9eceb887 100644
--- a/tests/slow/test_mcmc.py
+++ b/tests/slow/test_mcmc.py
@@ -74,17 +74,17 @@ def opn(fixture_path):
     ("analytical", None, "mcmc", None, True),
     ("analytical", None, "mcmc", "slice", True),
     ("analytical", None, "nuts_numpyro", None, True),
-    ("analytical", None, "nuts_numpyro", "slice", TypeError),
+    ("analytical", None, "nuts_numpyro", "slice", ValueError),
     ("approx_differentiable", "pytensor", None, None, True),  # Defaults should work
     ("approx_differentiable", "pytensor", "mcmc", None, True),
     ("approx_differentiable", "pytensor", "mcmc", "slice", True),
     ("approx_differentiable", "pytensor", "nuts_numpyro", None, True),
-    ("approx_differentiable", "pytensor", "nuts_numpyro", "slice", TypeError),
+    ("approx_differentiable", "pytensor", "nuts_numpyro", "slice", ValueError),
     ("approx_differentiable", "jax", None, None, True),  # Defaults should work
     ("approx_differentiable", "jax", "mcmc", None, True),
     ("approx_differentiable", "jax", "mcmc", "slice", True),
     ("approx_differentiable", "jax", "nuts_numpyro", None, True),
-    ("approx_differentiable", "jax", "nuts_numpyro", "slice", TypeError),
+    ("approx_differentiable", "jax", "nuts_numpyro", "slice", ValueError),
     ("blackbox", None, None, None, True),  # Defaults should work
     ("blackbox", None, "mcmc", None, True),
     ("blackbox", None, "mcmc", "slice", True),
@@ -137,7 +137,9 @@ def test_simple_models(data_ddm, loglik_kind, backend, sampler, step, expected):
 
     # Only runs once
     if loglik_kind == "analytical" and sampler is None:
-        assert not model._get_deterministic_var_names(model.traces)
+        assert f"~{model._parent}_mean" in model._get_deterministic_var_names(
+            model.traces
+        )
         # test summary:
         summary = model.summary()
         assert summary.shape[0] == 4