It’s very basic. When bolted together, the engine, bellhousing, and tranny become a beam. You want to fix the beam at two points only, meaning: front & mid mount or front & tail housing. If you were to fix the beam at three locations (front – mid – tail) somewhere along those 3 points will get stressed and most likely fail. You are not mixing solid and soft mounts in this case. The soft mount at the tail housing allows it to float and absorb any movement given the beam is already fixed at two points (front & mid) and the tranny is cantilevered. This is a typical configuration and works very well.
Mid Mount:
Front Mount:
