Maybe the easier, and less problematic way to handle this is to simply not allow it to happen.
CUT
Although maybe I am just old.
On one hand I can't really say I feel particularly invested in the topic of "nailing the sex scenes to perfection", but on the other hand I'm not sure what you are even attempting to argue here.
The game ALREADY allows sexual interactions between members of different races, like it or not, and some of these races may vary considerably in average size/physical structure. So at this point they may as well get the feedback/suggestions to do it properly.
