Do you need a surface reconstruction or is everything well mixed? If everything is provided via UDRGM so why requiring a VOF approach?

The issue is that the behaviour of the real problem is an intermediate between VOF and my model (VOF with a diffusive term). Consequently, I need a surface reconstruction at some specific zones, so I have to modify the diffusivity accordingly. At this point, two problem arise:n1) If I apply a source term (the diffusion term) to VOF, the solution changes almost nothing, while it should be equal to the result given by my model.n2) If I set D=0 for my model as a test (to see if it is equal to VOF), then the solver blows up.n