Been a match grip player for 10+ years and I'm now trying to learn trad. grip. I feel your pain with those rimshots. Feels like they will never come, but progress is happening.
For match grip, I used to kind of cheat... well not really, cause I know for a fact that Jeff Porcaro played this way... that is, using your leg to figure out where the rim is at. At first this was fine as long as my hi-hat foot wasn't moving, but I would kind of lose it when I was opening the hi-hat at certain times.
I basically have the same position still but I've gotten to the point where I can do it no matter what my legs are doing. I can do whole fills where every note is a rimshot. I can do them on the toms, timbales, practice pad, right hand, left hand, wherever, even the hi-hat gets a flat-stick once in a while. You just get better the more you do it. It's like a double-stroke roll or something, at first you can only do it a certain way, like on a very bouncy surface. But after a few years, it shows up on your leg, or floor tom, etc. Playing in a dance band gave me 3 hours per night x 50 - 75 nights per year to hone 'the rimshot'. Now I don't even think about it.
Get used to where your snare height is. I bring a tape measurer to gigs to get the stool, snare, and hi-hat just right.
And to the guy who mentioned lower tuning and triple flange hoops. I totally agree! Makes it way easier.
p.s. don't you guys hate it when a mentally deficient guitarist says "rimshot" when they mean "crosstick." Me too!!!