Groups are definately misleading unless you shoot arrow with black fletching and nocks.
Say you shoot one arrow at a spot and hit it, then the next time you shoot, your eye is naturally drawn to that arrow unless is less obvious than your spot and so on and so on.
Try to pick a spot a couple inches away from your arrow in the target and intentionally shoot just a couple inches away. Sure, it can be done, but it is much harder than grouping.
If you are honest with yourself, you should know if you hit the spot you are looking at. If you do it over and over then you are consistant even if you pick a different spot for each arrow.
I have never shot more than one arrow at an animal standing in the exact same location.
I have been shooting purely instinctive with a longbow for at least 6 years and a form of it for longer. I find that I only shoot well on 3D when I don't have a troubled or busy mind (hard to concentrate). I also find that shortly in to the round it is as much fun chatting with the other archers and less fun focussing. I have however shot well enough to win a few small tournaments of not more than 100 people in my class.
I have taken many deer and hogs out to 35 yards with out loosing more than a couple of deer and two hogs. I have not shot at every opportunity at either the farthest range or shortest because it didn't feel right too. Yes, I have missed too, including 3 out of 4 jumpy bucks in one night and on another night, I missed a rather calm buck 3 times only to kill another late in the evening.
All of the lost game were at under 15 yards. Cant quite say what happened there for sure but it wasn't an accuracy thing. Most of the game missed were under 20 yards.
Remember, with a referance shooting style, you must first estimate yardage. If you are off there, than being accurate can only be an accident or some instinct took over.
Nothing is perfect, all we can do is strive to do our best and take our best shot.
Many would do well to find one thing and stick with it. Rome wasn't built in a day and neither was a traditional archer.
good luck, BigJim