For those having trouble with the Bridge arc when sitting - sit pad.
Drape a foam sit pad over the arc edge - problem solved.
We use a 10"x20"x3/8" GG thin light foam sit pad. It could be smaller, but we just cut 10" off the end of a GG thin light pad and used it.
The problem, of course, is worse when wearing shorts. The pad cushions the arc and we no longer have a problem.