I just discovered that you can restrict the area a forest pack to a specific material id using the "Surf.Mat.ID" setting, which is totally brilliant. Then 10 min later I discovered that you can't apply a Falloff in the scale to the areas, as they don't seem to be recognised as edges of the material id zone, which is a bit of a pain. Only way I could get around it was to create a spline from the material id edge and restrict the FP using a spline area instead.
Is this a know bug/feature?
Forest version 5.3.0