Been trying this whole level streaming and Foliage seems to be the most pain in the a…ss part. I still have yet to figure out how to get multiple foliage layers without it merging by default.
However, the first step is purely asinine.
My suggestion is to make it like any other.
Double click layer, paint foliage, Double click next layer, paint foliage, now you have two different layers of foliage exactly where you want it and done.