When i am in the "mixer " screen, where i have access to all partials with their parameters, i dont need to use my knobs and buttons at the keyboard.
But when i am in the "envelopes" or " time slices" screen, i have no quick access to "FM Mod, FM Ratio etc.
So i would recommend to link a parameter (destination), for example "FM Mod", with one midi CC and let it only be active in the selected partial.
At the moment you can only select one control knob for one midi CC in the whole VST at all. See the picture attached.