Forget the rail effect for a minute. When a cueball hits an object ball, there's a full ball width target from half-ball hit on the left to half-ball hit on the right. Then on top of that there's another half ball on either side. So the normal collision "cross section" is 4.5 inches wide.
Ah, the joy of fat bullets. And so "rail reflection" can add a full ball's width or more to that (but little to none very near the rail).
pj
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