Rink grip size question

It looks like Rink is on holiday for a couple more days so I figured I would ask here and see if anyone knows the answer. I have a set of Medium Rink grips that are Convex, O degree and normal volume and they fit great except that I have to run the palm shelf almost all the way down. Because of this I was told to go to a large grip BUT I want to make sure the only dimension change between the med and the large is the length of the grip between the knuckles and not any of the volume around the grip? Does anyone here have an identical grip with one being medium and the other large?

Yes, I went through exact same issue. I was very happy with the M grip for my old GSP, except that I had to wind the palm shelf almost to the bottom, that left a gap between bottom of main grip and top of shelf which my pinkie would partially slide into, not perfect.
I tried LRB7 via Pardini USA, but could not get on with them. Not sure whether it was L size or the steeper angle or what. Happened that I still have my old GSP grip, when I put my hand in that it felt much better.
I recently received "GSP style upright" medium grips for my Pardini's with special order longer body wood to eliminate the gap. Works great so far.
Unfortunately, Rink only make "upright" versions for a few guns though. You need to check with Thomas.