To discriminate is to choose between things. That's what I am referring to here. Nothing to do with Spec or Gloss. More like blood/vein maps.

However; that is just going off into the weeds. One thing at a time. Did this answer your question about scatter depth on the Physical_Surface node? You realize that there must be depth to the mesh to get the effect. Scatter can't work on one sided mesh.

There used to be a bug in P11 when you had all three values set to the same amount. The effect rendered as though all three plugs were set to zero. It may or may not have been squashed. I haven't checked.

Adjust the depth to taste. It uses real world measurements and Poser's scale isn't exactly "real" so you will have to make minor adjustments as necessary.