Don't have a percentage, but mil movement seems to be the killer. Boxing is just hard to make decent grades in. DS's experience was that Loser gets a C+, winner gets a B-, if they both do everything right. And you can do worse.
I know of multiple plebes at risk of separation due to mil movement. You get two shots in the year at passing, then (apparently) a shot in the summer. If still no pass, you are separated.
More who did not get to take leave due to not being in good standing over mil movement.
DS came within a few points of supermaxing the APFT this semester, yet only made a B- in mil movement, which he thought would be a breeze compared to boxing. And fought hard for that!!!
I've not seen it in writing, but have been told that DPE has a different grading scale than the academics as well. Something is up for sure!
Similar for APFT. I know one plebe separated last summer over APFT, and two at risk this year. Just in DS's circle of acquaintances (company or sports) or those in our parents club.
The only saving grace for your CPS (cadet performance score) is that the individual academic, military, and physical averages are normalized statistically. So for many their adjusted average is higher than the raw average once std deviation is applied.
Don't mean to sound scary, it's just reality at USMA. If you are not fit you will be significantly challenged. And will get way more help than you can ever imagine!!!