Thanks for provided screenshots. In your case, I would suggest to use a slightly different work-flow - to create multiple Forest objects (for each type of vegetation) and mask its distribution.
By looking at your models, the previous example (one Forest object with multiple Areas using just selected models) isn't ideal for this purpose, as the Transform (Translation, Rotation, Scale) settings are shared. I must admit, the Composite map construction was in provided scene overcomplicated, but I was meant just to show it's masking / mixing possibilities. Please note, any map can be used as the Distribution Map (like previously prepared bitmap and so on).
Anyway, previously advised work-flow wouldn't be so flexible, when the size of vegetation differ and by splitting these items into several Forest objects you can control these Transform values individually.