I would also put down something that should also be on your list: sometimes the impostor has absolutely no way of separating a group of crewmates. If like 4 of them are in a stack against one impostor then they won, with little to no counterplay.
One fix I could think of is to have over 2 panels for the sabotages, then adjust the number of panels to visit based on the player count. then 4 players MUST separate from each other, then deduct the rest from there. That is just one solution, but if you find something better than do that.