I use off set, no matter the argument that's there's no such thing. I found, for me, 1/8 left was the smoothest, for my thumb. I don't come out to fast, don't hang up ( unless my thumb swells a lot) but that's not the pitch problem, that's my coffee problem.
It took me 4 balls to find the "right feel" for my pitch. I used an old ball, 1 3/8 thumb slug so I could adjust pitches without plugging, just a new slug.
It takes trial and error to get the 'prefect' feel for you.
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az guy aka: R & L Bowlers Pro
rlbowlerspro@cox.net