Why did it come up in the first place? Just read something last night that gave an extreme. It was a 3" rule. When paper tuning, a tear over 3"'s in either direction indicated a spine problem.

Here's part of the guide.

"Spine Assessment

If the arrow comes out of the bow with a large amount of rotation (very weak/stiff arrow) then you will get a very wide horizontal tear in the paper, the combination of the arrow vibration and its rotation. If this tear is too big its unlikely that any amount of bow tinkering or tuning will produce a good flying arrow and the arrow needs to be changed or replaced. Rick Stonebraker's tuning guide puts the maximum allowable horizontal tear at 3 inches. Any larger then this then a weaker/stiffer arrow as appropriate is required."