I have a student on quads that has been complaining of numbness in his knee after holding the drums for a while. I've got a friend who suffered from the same issue while marching corps and it actually caused some permanent damage. We're using the tube carriers so the belly plate is height adjustable. I believe the problem is that the plate sits right on the hip bone which cuts off blood flow to the legs, so I've been playing with moving the plate up and down in an attempt to get rid of the problem.

Anyone have any experience with this?

Dude-

Flip the plate upside down.

Yeah.

i agree try to get it as high up as you can and flip the plate.
if that doesnt work...seriously get a fiberglass vest harness if never had a problem with them other than alittle bruising on the hips

... Fiberglass vest carriers are hardly adjustable. Why would that be a more suitable option?

i really dont know but everyone on my line likes them
i personally dont
but we file the harnesses so that they are the exact length or shape to be comfortable for the player

OK so a little update. With the belly plate upside down, the brackets for the j bars are too high to set the drums at the proper height, he's a pretty tall guy. So flipping is not an option. At this point I'm thinking add some padding to get the pressure off of the side in question? He says he feels like the problem is in his shoulder, but I don't see that causing numbness in the knee. I believe one night he did try an old fiberglass vest we had kicking around, but those things are super uncomfortable and he didn't last long with that on.

If he's a tall guy, I would imagine the j bar brackets were in their lowest position? If so, move them to the highest one so when you flip it they are low again.

If there is only one set of holes for the bracket in the plate, consider getting a drill bit used for fine wood working (as to not damage the plate and create a smooth hole) and creating new ones.

I'm not entirely sure there's room to make new holes high enough on the plate, since there's those cutouts. I'll check it out