My rear seat jacks are mounted on top of the center tunnel between the back seat floorboards. Jacks point up (inserted downward). No issues with debris making them non-functional. In this position, mounting the jacks near the floor facing aft would increase the chance of stepping on them and breaking them off. Pointing up you would have to forget to remove them after flight, and really kick them hard to break or bend them.
If mounted on the side walls, the item in post #8 facing aft might make sense if it does not intrude on passenger space. I guess it really depends on where you are considering mounting the jacks, and what kind of space is available behind the jacks in those locations. In a Grumman, the floor tunnel location makes sense for a variety of reasons.