I stop exactly 19 inches from the foul line (at least i try to repeat it every time) every time I bowl, and have seen no consequences from it. i used to be right up next to the line, but I fouled once after having the front 8. This made me move back in the approach and stop short of the line. Every once in a while, if its dry enough, I will move up 8-12 inches just so that the ball gets through the heads a little better. As long as you're comfortable, and the ball isn't rolling out/ hooking too early, i think you're ok.
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stanski