archinicholas
So you'll want to select the vertices on the muscle/bone first and the fat second. This order is important because it determines the source/target for the attachment. When the source of the sliding attachment is the muscle/bone surface, it will leave the target (in this case the fat) free to slide between surfaces (which is what we want). Conversely, when the fat is the source, those vertices will only be able to slide over the target (muscle) this is not what we want.
The good thing about making the muscles/bones the sources for your attachments is that the target for the attachment pairs is the closest point on surface on the target mesh. Assuming that there's minimal intersections between your muscles/bones and the fat, then only the inside of the fat will be constrained.
Scene scale: I mean Maya units. Collision point spacing is measured in Maya units and is independent of the solver scale.
So changing your units between meters and centimeters for instance, while the collisionPointSpacing value stays constant, will populate your meshes with less or more points respectively.