I have just recently gone to a shorter span (over 3/8 shorter). The current span is fit according to the edge of the grip being at the midway point between the 1st and 2nd joint of my fingers.
My thumb went from 5/8 reverse and 1/8 right to 3/8 reverse and 1/8 right. I like how the relaxed grip feels but I am getting some rubbing and pain on my thumb. If looking at the thumb pointing up it would be on the right side of the thumb, right on the bone where the thumb widens. I have checked to see if I am squeezing the ball and I am not.. made sure I have been completely relaxed. Looking at my hand, as I close it, my thumb rotates putting this side of my thumb more on the surface of the hole that is in line with my finger holes.. before when I had a stretched span my thumb rotates the other way and put the flat side of my thumb more on the hole surface that is inline with the finger holes.. kind of hard to explain but I will try that.

is this something that I just need to get used to or is there a fix for this. I'm gonna try more bevel to the upper right side of my thumb hole to maybe allow my thumb to release in that direction.. more along the flat bottom side. Right now the bevel is more inline with the finger holes which is right where the side of my thumb is that is sore..

It could be a couple of things:

1. Your thumb pitch needs to go more toward the left if your thumb is rubbing on the right.

2. You may be turning your hand while your thumb is still in the ball, causing your thumb to twist against the side of the hole.

There is a callus building or already there.. there isn't a fear of the skin ripping but the actual bone area is sore or bruised..
I may need to get my thumb clear before turning.. but I don't think that is it.... where it rubs is pretty much lined up with how my thumb comes out of the ball.. in other words.. the side of my thumb that is rubbing is pretty much pointing toward the fingers whil my hand is in the ball.

I'll try to take pictures if that would show what I am talking about better.

In that case, you may need to move more forward... What is your span? 3/8 reverse is a good deal of reverse pitch unless you have pretty huge hands. If you had 3/8" of excess span, there's a good chance that you had more than 1/4" of excess forward pitch...

I was at 5/8 reverse.. now I am at 3/8 so we did go more forward.
My span is 5 inches.
Looking at how my hand moves going more forward would turn my thumb even more and put even more of the side of my thumb in line with the fingers.. I would say I would need more reverse to get my hand to open up and by thumb to be more on the flat underside.. but I know the reverse will probably cause me to squeeze.. so that is why I asked if it is something I have to deal with until I get used to it..

I have 1 ball where my thumb rubs slightly on the knuckle, just under the nail. I checked the span and pitch, and the are OK. I put 1 piece of black tape in the hole on the nail side, and it now is better, no rubbing.
Somehow, that hole must be a fraction off the other balls.

There is nothing that says the flat part of your thumb has to be at the top of the hole - on the contrary, most oval thumbs I have seen measurements for are around a 40* angle, which would have the top of the hole be about halfway between the flat part of the thumb and the side part of the thumb. I know that when I put tape in , to get it on the back of my thumb, I have to put it quite a bit to the left side of the thumb hole.

Your span is pretty long, so 3/8 might be ok... If you relax your hand, does the ball stay on? If so, you're good - if not, you should probably have more forward pitch. As jim said, that might need to be combined with a small move left (say, to 0 lateral)

I am the same way.. I put one piece of tape in the front of my thumb on the top right of the hole for grip.. and then other pieces in the back of my thumb on the bottom left side of the hole. Just the shorter grip has rotated my thumb so it hits the bone on the release..
The ball stays on when I completely relax..slips a bit but graps due to the angle of the thumb hole and the texture.. The ball grabs (rests) right on the point that is hurting.. maybe it is something I just need to get used to. M ybe new span is just rubbing and pushing on different parts of my thumb than I am used to.

I have tried 1/8 reverse and I had problems getting out of the ball. It might have worked with some more practice but the ball didn't seem to stay on my hand any better or be better fitting so I went back to the 3/8 reverse.