I find that having a tapered thumbhole allows me to have a really snug thumb fit but allows me to get out of the ball clean.
My thumb will be pretty tight when fully inserted but as it comes out about an inch the wider top allows the ball to release clean at the release.
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18 mph,350 rpm,PAP 5 1/2 x 3/8up, 10-13 deg axis tilt, varied rotational axis deg.. usually 45+
HighGame 300 x 5, High Series 808
Book Average 220,PBA Xperience 193