Each source is in which layer of the mesh?

I thought that when we use a five-layer mesh for generating the head model, some sources will be in gray/white matter and some of them will be in CSF. Am I wrong?
another question that I have is that when we use depth weighting with minimum norm imaging as a method and current density map as a measure, are we calculating weighted minimum norm estimate(wMNE)? If so, then what is the bst_wmne function? Does it do the same?