tk, I've done ton's of shooting from all distances. My first question is are you shooting at the same size targets? If so try shooting at a very small target at closer ranges. That will help you to pick out a better aiming point. Some guy's just shoot at the vitals on a target and dont concentrate on a small point. that should help some. Like you said, what you are having happen isn't normal. Not to disagree with anyone but fishtailing or plaining will only get worse the further out you get. give the smaller aiming point a try.
Jim