Um.. I thought a 5point haness must be properly mounted ie to a rollcage... if you look at how your factory seat belt has a pivot point higher than your shoulder, theres a reason for that.. if you get into a front end collision, the seat will not crush, or collapse on you.. if your belt mounting points are lower than your shoulder, your asking for trouble.. look at all the cars who race, all their 5 point harnesses are mounted equal or higher than the drivers shoulder.... if you want good support get a good seat...
my 2 cents