The Morich guide is what I use and would really recommend you stick with this. the pitch of the fingers is primarily determined by your span. Think of these extreame examples and it may help
1. Lets say a 3 yr old comes in to your Pro Shop
and wants a bowling ball drilled, with such a small span (lets say 2 inches) you really need both the thumb hole and finger holes angles toward each other (forward forward) this will give sort of a suitcase grip so the child can hold onto the ball without dropping it. Any reverse with either the fingers and/or the thumb would require a super strong deathsqueeze on the ball, only superman baby could hold onto the ball.
2. Next the Jolly Green Giant comes in with his 12 inch span hand and he wants a ball drilled up. Since his span is so long, drilling the ball with zero pitch in both thumb and finger would have the fingers and thumb pointed at each other. Assuming the thumb is fully inserted into this bowling ball, it would be physically impossible to even put fingers into the finger holes unless you had super flexible rubberband fingers.
The correct thumb pitch is what will keep the ball in your hand and not flopping around. Finger pitches really are just a comfort thing but changing span is a better idea, alot of reverse in your fingers and your gonna loose revs and having to squeeze on the ball.