diff --git a/include/common/SolutionRecorderImpl.hpp b/include/common/SolutionRecorderImpl.hpp
index bc245c1ed..4e43b7e24 100644
--- a/include/common/SolutionRecorderImpl.hpp
+++ b/include/common/SolutionRecorderImpl.hpp
@@ -339,7 +339,7 @@ class InternalStorageUnitOpRecorder : public ISolutionRecorder
 		if (!_storeCoordinates)
 			return;
 
-		if (!_axialCoords.empty())
+		if (!_axialCoords.empty() && ((_keepBulkSingletonDim && (_nAxialCells == 1)) || (_nAxialCells > 1)))
 			writer.template vector<double>("AXIAL_COORDINATES", _axialCoords);
 		if (!_radialCoords.empty())
 			writer.template vector<double>("RADIAL_COORDINATES", _radialCoords);
@@ -350,7 +350,7 @@ class InternalStorageUnitOpRecorder : public ISolutionRecorder
 			unsigned int offset = 0;
 			for (std::size_t pt = 0; pt < _nParShells.size(); ++pt)
 			{
-				if (_nParShells[pt] == 0)
+				if (_nParShells[pt] == 0 || (!_keepParticleSingletonDim && (_nParShells[pt] == 1)))
 					continue;
 
 				oss.str("");
@@ -882,7 +882,9 @@ class InternalStorageUnitOpRecorder : public ISolutionRecorder
 		{
 			oss.str("");
 			oss << prefix << "_VOLUME";
-			writer.template matrix<double>(oss.str(), _numTimesteps, _nVolumeDof, _curStorage->volume.data(), 1);
+			// Note: since the CSTR is currently the only unit operation that simulates volume, and _numVolumeDof is 1, we always write this as a vector.
+			// Once other unit operations are implemented with more than one volume, we should add the option here to write this as a matrix (singletonDimension filed etc, see other output).
+			writer.template vector<double>(oss.str(), _numTimesteps * _nVolumeDof, _curStorage->volume.data(), 1);
 		}
 	}
 
diff --git a/src/libcadet/model/StirredTankModel.hpp b/src/libcadet/model/StirredTankModel.hpp
index 61eb1cc4a..dc720b997 100644
--- a/src/libcadet/model/StirredTankModel.hpp
+++ b/src/libcadet/model/StirredTankModel.hpp
@@ -191,7 +191,7 @@ class CSTRModel : public UnitOperationBase
 		virtual unsigned int numInletPorts() const CADET_NOEXCEPT { return 1; }
 		virtual unsigned int numOutletPorts() const CADET_NOEXCEPT { return 1; }
 		virtual unsigned int numParticleTypes() const CADET_NOEXCEPT { return _nParType; }
-		virtual unsigned int numParticleShells(unsigned int parType) const CADET_NOEXCEPT { return 1; }
+		virtual unsigned int numParticleShells(unsigned int parType) const CADET_NOEXCEPT { return 0; }
 		virtual unsigned int numBoundStates(unsigned int parType) const CADET_NOEXCEPT { return _strideBound[parType]; }
 		virtual unsigned int numMobilePhaseDofs() const CADET_NOEXCEPT { return _nComp; }
 		virtual unsigned int numParticleMobilePhaseDofs() const CADET_NOEXCEPT { return 0; }