A. There is no such thing as any sort of off set...it's a round object therefore they are angles and lines
B. perfect scenario is one where the fingers seat properly into the gripping holes and the thumb is able to enter and exits the thumb hole with forced deviation -
The ways I obtain these are as such - span dictates angles not visa versa
If you have an already drilled bowling ball, place the thumb in the thumb hole, over lapping the fingers over the finger holes; the appropriate crease shoud dissect the gripping hole - yes there is a minimal amount of give & take, allowing flexibility and feel
Once a desired starting span is acquired, the next factor is flex and how the thumb hinges; angles are created to allow proper gripping as well as the hand, primarily the thumb to exit the thumb hole due to gravity and acceleration, not the bowler have to manipulate their hands to 'let go of the ball'.
A way to check is how the digits enter the bowling ball and react to gripping the ball; with the fingers you do NOT want to see any stress on the knuckles or finger nails, they should be properly seated in the gripping holes, not forced into any angle other than naturally.
Part 3 (span & fingers) is how the thumb enters the thumb hole, as well as allowed to exit, so with the fingers properly seated into the gripping holes, start the thumb into the thumb hole, if the hole is at the proper angle, the thumb is allowed to enter without deviation.
Another variable is grip strength as well as wrist strength...when the wrist is in the proper position, this minimizes grip pressure and/or the necessity to grip the ball to hold onto...the weaker the wrist, the increase in gripping.
Hopefully this makes sense...