One problem I have had when solving the short-draw locking-up problem is substituting one problem for another. I lock up because something about completing the shot makes me nervous. I can make myself come to full draw if I focus on that aspect of the shot alone, but the nervousness doesn't go away. So "I shoot terrible when I do it," because rather than short drawing, the nervousness shifts someplace else, and I begin to tense my bow hand or string hand/forearm, pull the release, or something else.
The real solution is to get rid of the underlying nervousness, which Clickerman or Kidwell can certainly help with. But while you're working on that, also look for other errors that might be creeping in that make you shoot terrible, and solve them one by one. This is a useful, though frustrating exercise, because it probably won't occur to you that you could be tensing your string forearm if you haven't been doing that before, but once you learn to recognize it, it becomes much easier to correct in the future.