I believe it even helps if you get plain round black targets--under many lighting situations, they make it very difficult if not impossible to see your hits. That in turn helps keep you from looking for them...and takes your focus away from the target. Most new shooters want to see where they hit immediately after the gun goes bang, and unfortunately, many want to know before the gun goes bang. It's natural, and a natural killer of good shooting. You will hit the target exactly where the gun was pointed when it went bang--your challenge is simple: know where the gun was pointed when it went bang. It's NOT simple, really--if it was, we'd all be expert marksmen.
At the range I often see folks use those goofy targets that show where you've hit in iridescent green or orange, and they can't avoid looking at that kind of target. I think they're the worst gimmick there is for learning to shoot, and strongly recommend not to use them. Other folks fire 3 shots then run the target back to the firing line to look, then run the target back out, 3 more shots, etc. It's ridiculous, and counterproductive. Some instructors simply take the target and reverse it so you're shooting at a blank piece of paper--again, the same reason, to take the shooter's focus off the target and where the hits are being made. I prefer to have the target to hold the sights on, but as mentioned, focus is on the front sight.
"Too little trigger finger" means the just the tip of the finger is positioned on the trigger, which tends to push the gun to the left. "Too much finger" means the index finger is wrapped over the trigger, maybe even to the first joint, and that tends to pull the gun to the right.
Dry fire practice is your friend. Using extreme care to ensure safety (such as no live ammo in sight), cock the gun and practice holding on a target pinned to the wall, etc., and press the trigger while focusing on that front sight. Keep both eyes open until after the trigger breaks--the objective here is two fold: 1) press the trigger until it breaks without moving the sights, and 2) keeping the eyes open through the break--you must be able to see the sight picture when the trigger breaks. Do that about 5 million times.
Then, next time at the range, do exactly what you did in dry fire practice. It isn't easy, but when you succeed, you will get excellent hits.
Last tip: avoid loading 15 rds in the magazine and then feeling compelled to empty the mag into the target one after the other with no break. Lots of folks do this, and the 'groups' they make show it. Generally, muscle fatigue sets in immediately, and visual acuity is the very first thing to go--and it goes fast. Closely related to this is bringing the gun up and holding it in position for 20, 30 or 40 seconds waiting to get the good shot. It just isn't going to happen for the same reason. Shoot at a slow rate, but each shot itself shouldn't drag out for more that 5-10 seconds at the most. The longer you hold that gun out there, the less likely it is you can hold that gun out there.
You've already taken the time to observe your own shooting and to compare your performance between your various handguns. That's good--you've eliminated the arrow as the problem and concluded it's the Indian, as they used to say. It usually is--not always--but usually.
