The reason why most of the pros use 2-3 (at the most) different layouts is because generally, most, that are with a certain ball company, realize that bowling balls are designed with certain reaction characteristics in mind. Thus, if you are using a set layout, that you basically know how it reacts or responds, you are using a combination of a consistant, proven reaction and taking a reaction characteristic in a bowling ball to get better results. If you do not know, truly, how a bowling ball is going to react, why compound it with trying a new layout as well.
As many of the pros that I have worked with....I have tended to stay in a parameter of high 4" to 6" pin to PAP, either above or below, PSA/mass bias' in the 30-60 degree range, as well as allowing for a weight hole to adjust reaction. I also tend to use weight holes in PSA/mass bias to enhance overall reaction.
REMEMBER keep it simple. Ball and coverstock type is A number 1 in aquiring proper overall reaction. Layout and weight hole is a compliement or enhancer.
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Formerly BrunsRico