Remember this also, if you have the chance to throw the ball before adding the extra hole, do so. See how it reacts, legal or not (non-competition), then determine what you would like to see the ball do. If you would like more reaction in the midlane and backends, as it sounds like you do, place the hole approx. 5-6" right of your grip and 1-2" down. This would create a stronger flaring reaction, thus making the ball stronger in the right place on the lane. If by chance you need the ball to arc more downlane, place the hole 4-5" right and 1-1 1/2" up. This will reduce the flare and give the ball a smoother look.
RoB LAW (not as smart as MR.CeeGee Nomadda, but he's learnin' me sum)
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If ya ain't throwin' Brunswick.....Ya ain't maximizin' your abilities. Get ur done with Brunswick !!!