diff --git a/src/sp2xr/helpers.py b/src/sp2xr/helpers.py
index 2718d22..a2278fc 100644
--- a/src/sp2xr/helpers.py
+++ b/src/sp2xr/helpers.py
@@ -34,8 +34,8 @@ def load_and_resolve_config(args):
         "do_BC_hist": get(base, "workflow.BC_hist", False),
         "do_scatt_hist": get(base, "workflow.scatt_hist", False),
         "do_timelag_hist": get(base, "workflow.timelag_hist", False),
-        "rho_eff": choose(args.BC_rho, base, "bc.rho_eff", 1.8),
-        "BC_type": choose(args.BC_type, base, "bc.type", "constant_effective_density"),
+        "rho_eff": choose(args.BC_rho, base, "bc.rho_eff", None),
+        "BC_type": choose(args.BC_type, base, "bc.type", None),
         "cluster": {
             "use_local": choose(args.local, base, "cluster.use_local"),
             "cores": choose(args.cores, base, "cluster.cores", 8),
@@ -177,14 +177,12 @@ def parse_args():
     )
 
     # BC proeprties
-    p.add_argument(
-        "--BC_rho", type=float, default=1.8, help="BC density (default: 1.8)"
-    )
+    p.add_argument("--BC_rho", type=float, default=None, help="BC density")
     p.add_argument(
         "--BC_type",
         type=str,
-        default="constant_effective_density",
-        help="BC type (default: constant_effective_density)",
+        default=None,
+        help="BC type",
     )
 
     # cluster / resource knobs (all optional)