Practice at long range is great. I whole heartedly advocate it. It's also a lot of fun. That said, your problem seems to me to be a lack of ability to focus. Use your busy target and learn to ignore everything except the ONE SPOT you're aiming at. You need to learn to block out distractions. I shoot a five-spot target worse than a one spot as my eye wants to wander to the middle of the target. Therefore I practice with the five spot to train myself to focus on the one target that I want to hit. I've gotten much better at hitting the corner targets.