George, PM me your snail mail address and I'll fix you up with some proper-sized 10 meter targets. (This offer good for everybody else, too.) The targets I'm pretty sure you're using are too small. The ones marked "Airguns of Arizona" are too small for me (although I'm sure they're properly scaled. Maybe the dot becomes proportionately bigger but they just LOOK tiny.) The important thing, I think, is to have targets that duplicate the sight picture of the real thing, so that when you get in the match it all looks familiar.
If you must score, just pick a system you're comfortable with, one you won't second-guess. I call an edge shot a hit if half the pellet is on the target, ties go to the shooter. But, as you realize, this training is not about score. We keep track of score because WE JUST CAN'T HELP IT! But we have to remember we're training for performance, not score. A jerked shot that hits the target is still a bad shot. The big thing the airgun does is let us folks with families and jobs handle the gun and shoot at least a little every day. What we are doing is making the process of lifting, loading, shouldering and getting into position a subconscious process. Eventually (and it's taking me forever) we have more attention to devote to the shot. When follow-through becomes subconscious we've accomplished something important and the airgun sure lets you know when the follow through isn't good.
The neat thing about frequent practice is that it keeps you in a state of feeling that you're RIGHT ON THE VERGE of a breakthrough! Actually, the average score just creeps up but, hey, if this were easy, everybody would be doing it.