Thumb with too much reverse and/or lateral pitch?
Thumb hole too large?
Could be a combination of several things. After having as much as 3/16 reverse and 3/16 left a few years ago, I have gradually come back to zero and zero. I don't need nearly as much grip pressure as before. I haven't had any issues with the thumb not exiting cleanly, either.
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Lane Carter, Strike Zone Pro Shops - Salt Lake City, Utah