okay glad that’s clear, wasn’t sure that was the source of the confusion 
your layers blend nicely when you brush them thanks to the HeightBlend option. this is nice and all, but it’s nothing procedural (all it does is to “bias” the weight of the painting towards one layer or the other, based on the texture’s heightmap - so that the blending of the layers is more natural). this is the kind of stuff that can be described as “small, cool details” and something I’ll definately look into in the future, but at the moment I’m only worried about the grand scale of things (where the different ground types appear and why, procedurally)
I guess you mean this] ? I haven’t used this feature yet so I had forgotten about it (long time UE3 user, this is new from UE4). but if each of the layerblended materials can have a different PhysMat then it could very much benefit my material
I’ll definately play around with the LayeredMaterials feature for this, thanks for the tip