You might also experiment with your left/right pitches. I am right-handed, and left pitch lets me clear the thumbhole earlier, while right pitch makes me stay in the ball a bit longer.
Right now, I have reverse pitch in my thumbholes also, so I have to keep them very tight, but pitching it just a bit right ( under palm ) could help, as long as you can still clear the thumb without hanging up in it.
I have also gone to using oval thumb sleeves instead of round ones. This has not only helped me throw the ball better, it has made putting a proper thumb-hole in my ball as easy as drilling the span right and drop in the sleeve! Used to take DAYS to get one perfect, now it takes just minutes, and I have as godd, if not better, feel than I've had in the past.
--------------------
"TOO SOON THE POWER, TOO LATE THE WISDOM"