I'm with Simon. Forget about the target for a while. Or rather, don't throw the kick at the bag for a while. Just go through that chambering motion but don't actually throw the kick. I think Simon's right that, if you're delivering a kick, you tend to fixate on whatever your image of a well-delivered kick is. The satisfying "thwack!" of the bag or thai pad, etc. And you inadvertently compromise form in order to get that result. I think that likely explains your tendency to lean forward as well. One of the things that a past kickboxing coach had us do is spend one round of shadow boxing chambering for a kick without actually throwing it. So we'd throw the punches, and concentrate on the transition points from punching to the setup for the kick. And again back to the punching. I've sometimes taken that one step further and done rounds where I don't even throw punches. I just concentrate on the foot placement and hip/shoulder motions without throwing the actual punch. You kind of see boxers doing something similar when they're warming up for a bout. They throw these very loosey goosey punch combinations to warm up. But they're going through the hip and foot motions without throwing actual punches. I'm a huge advocate of footwork. To me, foot placement is what makes ALL other things credible. The difference between performing a hook punch and causing someone to double over in undignified agony generally begins with the feet.