diff --git a/src/AdvectionSimulation.hpp b/src/AdvectionSimulation.hpp
index 51e1706ad..dcb8959b2 100644
--- a/src/AdvectionSimulation.hpp
+++ b/src/AdvectionSimulation.hpp
@@ -152,6 +152,7 @@ template <typename problem_t> void AdvectionSimulation<problem_t>::setInitialCon
 {
 	// default empty implementation
 	// user should implement using problem-specific template specialization
+	// note: an implementation is only required if face-centered vars are used
 }
 
 template <typename problem_t> void AdvectionSimulation<problem_t>::computeAfterTimestep()
diff --git a/src/HydroBlast2D/test_hydro2d_blast.cpp b/src/HydroBlast2D/test_hydro2d_blast.cpp
index 8b17eb0d7..f16efbea7 100644
--- a/src/HydroBlast2D/test_hydro2d_blast.cpp
+++ b/src/HydroBlast2D/test_hydro2d_blast.cpp
@@ -27,7 +27,7 @@ struct BlastProblem {
 
 template <> struct quokka::EOS_Traits<BlastProblem> {
 	static constexpr double gamma = 5. / 3.;
-	static constexpr double mean_molecular_weight = C::m_u;
+	static constexpr double mean_molecular_weight = 1.0;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
@@ -169,7 +169,7 @@ auto problem_main() -> int
 	sim.stopTime_ = 0.1; // 1.5;
 	sim.cflNumber_ = 0.3;
 	sim.maxTimesteps_ = 20000;
-	// sim.plotfileInterval_ = 2000;
+	sim.plotfileInterval_ = 2000;
 
 	// initialize
 	sim.setInitialConditions();
diff --git a/src/HydroKelvinHelmholz/test_hydro2d_kh.cpp b/src/HydroKelvinHelmholz/test_hydro2d_kh.cpp
index 59b714a67..3cb6373e1 100644
--- a/src/HydroKelvinHelmholz/test_hydro2d_kh.cpp
+++ b/src/HydroKelvinHelmholz/test_hydro2d_kh.cpp
@@ -24,7 +24,7 @@ struct KelvinHelmholzProblem {
 
 template <> struct quokka::EOS_Traits<KelvinHelmholzProblem> {
 	static constexpr double gamma = 1.4;
-	static constexpr double mean_molecular_weight = C::m_u;
+	static constexpr double mean_molecular_weight = 1.0;
 	static constexpr double boltzmann_constant = C::k_B;
 };
 
@@ -84,7 +84,6 @@ template <> void RadhydroSimulation<KelvinHelmholzProblem>::setInitialConditions
 		state_cc(i, j, k, HydroSystem<KelvinHelmholzProblem>::x2Momentum_index) = rho * vy;
 		state_cc(i, j, k, HydroSystem<KelvinHelmholzProblem>::x3Momentum_index) = rho * vz;
 		state_cc(i, j, k, HydroSystem<KelvinHelmholzProblem>::energy_index) = P / (gamma - 1.) + 0.5 * rho * v_sq;
-		state_cc(i, j, k, HydroSystem<KelvinHelmholzProblem>::internalEnergy_index) = P / (gamma - 1.);
 	});
 }
 
@@ -122,7 +121,7 @@ template <> void RadhydroSimulation<KelvinHelmholzProblem>::ErrorEst(int lev, am
 
 auto problem_main() -> int
 {
-	// Boundary conditions
+	// Problem parameters
 	const int ncomp_cc = Physics_Indices<KelvinHelmholzProblem>::nvarTotal_cc;
 	amrex::Vector<amrex::BCRec> BCs_cc(ncomp_cc);
 	for (int n = 0; n < ncomp_cc; ++n) {
@@ -135,7 +134,7 @@ auto problem_main() -> int
 	// Problem initialization
 	RadhydroSimulation<KelvinHelmholzProblem> sim(BCs_cc);
 
-	// sim.stopTime_ = 1.5;
+	sim.stopTime_ = 1.5;
 	sim.cflNumber_ = 0.4;
 	sim.maxTimesteps_ = 40000;
 	sim.plotfileInterval_ = 100;
diff --git a/src/RadhydroSimulation.hpp b/src/RadhydroSimulation.hpp
index 1f9e4c322..150c37cb4 100644
--- a/src/RadhydroSimulation.hpp
+++ b/src/RadhydroSimulation.hpp
@@ -482,6 +482,7 @@ template <typename problem_t> void RadhydroSimulation<problem_t>::setInitialCond
 {
 	// default empty implementation
 	// user should implement using problem-specific template specialization
+	// note: an implementation is only required if face-centered vars are used
 }
 
 template <typename problem_t> void RadhydroSimulation<problem_t>::computeAfterTimestep()
diff --git a/src/simulation.hpp b/src/simulation.hpp
index 29893e681..722408c26 100644
--- a/src/simulation.hpp
+++ b/src/simulation.hpp
@@ -355,7 +355,7 @@ template <typename problem_t> class AMRSimulation : public amrex::AmrCore
 
 	// Nghost = number of ghost cells for each array
 	int nghost_cc_ = 4; // PPM needs nghost >= 3, PPM+flattening needs nghost >= 4
-	int nghost_fc_ = 2; // at least 2 are needed for tracer particles
+	int nghost_fc_ = Physics_Traits<problem_t>::is_mhd_enabled ? 4 : 2; // 4 needed for MHD, otherwise only 2 for tracer particles
 	amrex::Vector<std::string> componentNames_cc_;
 	amrex::Vector<std::string> componentNames_fc_;
 	amrex::Vector<std::string> derivedNames_;