Let me start by saying that this is just speculation. However, the people I know who are very good at instinctive shooting don't try to fool their brains by focusing on a spot higher than the one they want to hit. I mean, it's your brain, so it knows what you're thinking. When you get beyond the distance that instinctive works for you, why not just shift to gap?
However, this doesn't solve your left misses on quartering away shots. Left misses on one side wouldn't be too bad, as you want to hit a little further back on an animal quartering away to your right. On an animal quartering away to your left, a left miss could be disasterous. I would guess this is a result of target confusion, where you really need to pick a spot that is different from the spot you would pick on a broadside animal. Further left on an animal quartering away to your right; further right on an animal quartering away to your left. Maybe this is your brain getting even with you for trying to fool it on 30 yard shots?