diff --git a/pyciemss/integration_utils/intervention_builder.py b/pyciemss/integration_utils/intervention_builder.py
index 30345d16..e6049150 100644
--- a/pyciemss/integration_utils/intervention_builder.py
+++ b/pyciemss/integration_utils/intervention_builder.py
@@ -78,7 +78,7 @@ def start_time_param_value_objective(
     def intervention_generator(
         x: torch.Tensor,
     ) -> Dict[float, Dict[str, Intervention]]:
-        assert x.size()[0] == param_size * 2
+        assert x.size()[0] == param_size * 2, "Size mismatch: check size for initial_guess_interventions and/or bounds_interventions"
         static_parameter_interventions: Dict[float, Dict[str, Intervention]] = {}
         for count in range(param_size):
             if x[count * 2].item() in static_parameter_interventions:
diff --git a/tests/fixtures.py b/tests/fixtures.py
index 55daf4d4..9d2d7580 100644
--- a/tests/fixtures.py
+++ b/tests/fixtures.py
@@ -124,9 +124,9 @@ def __init__(
     "static_parameter_interventions": start_time_param_value_objective(
         param_name=["p_cbeta"],
     ),
-    "objfun": lambda x: -x,
-    "initial_guess_interventions": 1.0,
-    "bounds_interventions": [[0.0], [40.0]],
+    "objfun": lambda x: -x[0] * 0.25 / (0.0 - 40.0) + np.abs(0.35 - x[1]) * 1.0,
+    "initial_guess_interventions": [1.0, 0.15],
+    "bounds_interventions": [[0.0, 0.1], [40.0, 0.5]],
 }
 
 optimize_kwargs_SEIRHD_param_maxQoI = {