Just read a user comment bemoaning the lack of a volume balance control for the layers (if the two VCA envelope level sliders aren’t felt to be sufficient for this purpose).
Could a shift function be perhaps added to the master volume knob to give it a layer balance function? (The Prophet 5/10 added this. It works pretty well, you just need to be wary of moving it when it reverts to normal function and is set high if knobs are in jump mode. Another good case for adding a pass-through knob mode?)