We looked at a lot of different options when designing our connectors. I don't think that we ever considered plugging into the back of the torsion bar slot, however that would be a lot of forces acting on the one part of the forward subframe. If it just plugged into the back of the socket I don't think that you would get a lot of fore-aft "anti banana" resistance. Couple that with the inconsistent depth that various manufacturers bars seat into the socket and I'm not sure that it would work out as well.
We made the forward end of the connectors modular because there are light inconsistencies on how much various cars have "settled" over the years. I've put these connectors in a LOT of cars and no two have been the same, and most require a bit of persuasion.