Mike, Taylor and I used to do that too, for decades and with excellent results.
When my big girl was shooting sub 2" groups at 100meters that is the method I used.
Then I day, I thoguht about the slightly crooked thump I was giving the ball with my starter knob - what if? So I experimented with a strip of patching material, thumped in a ball as normal then pulled it out and checked it visually.
Lead was oviously pushed up on one side more than the other by the lands, ie: the rifling marks were deeper on one side than the other, with a small ridge of lead above the heavier imprint. I did it again and again to check this finding and indeed, I found it almost impossible to start a ball perfectly straight, with perfectly even rifling marks left on the ball by thumping it in with the starter's handle and a hand blow. For hunting large game, the difference in accuracy would be negligible, however, for accuracy shooting - it ALL matters.
That is when I went to the short nub on the starter's handle for straighter line seating, and even then, one must be careful. I did finally find perfectly imprinted balls when checking the seating alignment with this method, so since I've become accustomed to it, I use it.
I am sure today, that round ball bench rest shooters, if allowed, would be or are using muzzle fitting, in-line ball seaters for a perfect seat into the lands of the patched round balls, especially if false muzzles weren't allowed. It makes sense to seat the ball as perfectly as one attempts to seat an elongated bullet.
