the voice modes on MP are basically rotating allocators, so there is no explicit assignment per row.
any row has a chance to occupy any of the four voices in four-voice mode. if MP is on “toggle” mode this becomes much clearer to see, when there are more held notes. typically in the trigger/blip mode there aren’t very many overlaps, so most of the notes go out voice 1 or maybe voice 2.
i’m trying to imagine a voice assignment application-- are you thinking of rows split to specific voices? short of modifying the firmware, you could do this quite easily with Teletype, though it’d be a lot of patch cables.