Heat flux BC in axisymmetric case

kevin

I am modeling a simple cylinder using an axisymmetric mesh. I have added a heat flux BC at the top boundary with a DEFINE_HEAT_FLUX UDF. The heat flux profile is a top-hat extending a distance r0 from the symmetry axis. The heat enters the mesh in the axial direction. However, when I run this case in steady state, the solution never converges despite mesh refinements and adjustments to the relaxation parameters. When I run the same UDF in a 3D model of the same geometry there is no problem. Do I need to add something to the UDF to account for the axisymmetric nature of the problem? Thanks!