What Arne says is certainly correct. Hitting the target is a future event until you have done it, and then it is a past event. Even at the exact moment in the present when the arrow hits the target, the arrow has left your bow and it is too late to do anything about it. So thinking about hitting the target is never going to help you to actually hit it; all it is is a distraction from the things that actually will help you to hit the target, which are those things that Arne mentions.
However, going one step beyond the things Arne mentions, how does a person actually do those things, as opposed to merely wishing that he were doing them? As you say, you do them pretty well in practice, but it is more difficult to do them in a tournament. I would go further and say that it is sometimes easy to do them in practice, and other times not so easy. Why?
The answer is loss of concentration, in a tournament because of pressure, in practice because of boredom. Once a person learns the fundamentals, his job from that point on is to apply the rules he already knows to each and every shot. This is a mental challenge much more than a physical challenge. Learning to concentrate is the most difficult and useful skill you will learn as an archer. We learn concentration as a means of becoming better and more consistent archers; archery is included as one of the paths in Zen as a means of learning better and more consistent concentration.
This is a lifelong commitment. It would be a mistake to think that you could learn to concentrate like you learn to use back tension, and then go on from there. A start would be to adopt Rod Jenkins' philosophy of never accepting less than a perfect shot. When you step up to the line, whether in practice or at a tournament, you have to close out all distractions, whether pressure or boredom, with the attitude that THIS shot is the most important thing I have to do at this moment in time, and if at any point during the execution of it, I notice it going south, or my mind drifts to something else, I will let it down and start again.
Can I always do that? Not by a long shot. But I know that if I want to get better, that is my path to improvement.