The exit hole is recessed backwards and squareish, with a wide channel. The flange doesn’t sit properly inside it, and the circumference of the bell is too small. With the beehive the circumference is wider, and it just sort of smothers the whole area, and pumps the water through its center hole, which has nowhere to go but into the exit. Like, it’s not anything precise, it would probably work great in a “normal” toilet just as well because it just fills whatever space there is.