Increasing crunches w/ slight training issue (personal)

Looking for advice. Been in the DEP since October. I ship to boot camp in August. My PFT is decent: 19:01 / 21 pull-ups / but the issue is my crunches: 85 (as of this morning)

I have never gotten above 96 crunches. I have a problem training with crunches and russian twists alone because I have an elongated tail-bone that rubs the skin raw at the top of my buttocks every time I do a max set of crunches or pyramid set of russian twists. Yes, it really sucks. I am medically cleared by MEPS so it's not an issue other than training for the PFT.

I really want to get to 115 crunches. I have trained other ways, primarily through flutter kicks, leg raises, but they really haven't helped my max crunches.

I'm 6'1" and 190lbs. I know I can't be the only tall(ish) person having problems with crunches.

Thanks in advance.