Having a Christmas Eve eggnog and thinking out loud here. The part of the patch around the ball that goes in the rifling doesn't know if it is centered on the pre-cut patch or not. It should go in the same each time. The bunching would be above the ball and might be off center some but should part company with the ball upon exiting the muzzle. Cutting from a strip of material at the muzzle is about the same as an off-center patch as far as bunching is concerned, but cutting removes the bunched patching (or at least makes it equal and nice looking) all the way around the ball. Bunching is just more visible on a pre-cut patch because we can't trim it off. Since I just shoot for fun and some deer hunting, I will use my pre-cuts and let the loose ends drag.
Too much eggnog last night therefore, I hope my typing is more clear than my vision ... and/or thinking.
For those inclined toward "PII" (Col. Coopers "Preoccupation with Inconsequential Increases"), one can make a starter from a block of wood with a round ball dimple in it.
Lay your patching across the muzzle and using "the block", short start the ball to just past the "equator", now without nicking the ball, cut the patch and there will be NO material bunched or wadded above the ball and the patch will be perfectly centered.
One could also vary the depth of the dimple to adjust just how much material remains above the "equator" until they get the results desired.
As mentioned previously, MY shooting ability (or inability) does not warrant that much experimentation.
Now, who has slo-mo footage of multiple PRB's being fired with a
full charge of powder so we can ascertain where the patch parts company with the ball?
Cheers,
Smoketown