Ah, the legend of the "shelf butt", lol!
Some women found it happening to them when doing a lot of tall box presses. Not sure if they were doing the mid-era Firms (mid to late 90s aka the Tracie Long years) or the Goodtimes (GT) Firms (BSS-1, BSS-2), but those workouts used the tall box in virtually every workout.
I was never much into either the mid-era or GT Firms, but the classics (vols 1-6) had
substantially less tall box, which wasn't even introduced until Vol 3 (and
that volume had very little), so I wouldn't even worry about it with the route you're going.