I?ve debated on going through the hassle of having an after-market backrest installed on my Permobil F3, which I know will require the mounting hardware in order to do so. I just don?t feel like I?m getting enough lateral support with the standard cushion with the lateral supports. The biggest concern I have though in doing so is losing seat depth. I?m 6?4?, and probably 6? of that is legs, so I can?t afford to lose much, if any, seat depth. For those with after-market backs, how much more lateral support do the mid-depth cushions have compared to the standard backrest? I?m concerned the deep back might be too deep, but not sure. Also, I do not like anything interfering/hitting my shoulders.