The receded jaw player on the other hand is likely to have his upper lip contact the inner rim edge at a much more pointed connection. For him a sharp bite is anathema. It sure was for me. The idea of playing a long lead gig with lots of high notes in similar league (to me) as walking on glass.
I don't even like flat rims for the same reason: The flatter rim causes my upper lip to bend more severely at the junction of the "bite" or inner rim edge. Thus I use Al Cass pieces for EVERYTHING I do. All his pieces from tuba to French Horn have a continuous radius from outside the rim to inwards. A well rounded bite and neither too wide a rim contour nor too thin. Just about right.
If it weren't for Al Cass I'd be just another run of the mill trumpet player. Or I might even have quit playing except as a hobby. I hate to think of how depressed I might have become had I never found his pieces nor took his brass clinic way back when.
Ya know from that angle i suppose you could say that Al Cass may have saved my life. We met back in 1976 over a six pack of warm Esslinger beer. A six pack EACH lol. He always drank it warm God knows why.