I've fought with short drawing for a long time. It's just as much a confidence problem as it is a shooting form problem. Mine started when I tried to shorten my draw length and I lost concentration and pulled too far. The point of the arrow fell behind the shelf and wedged between the string and my hand. After that, I was afraid of doing it again.

Without an arrow on the string, I can draw and anchor with absolutely no problem, whatsoever. With my eyes closed, I can load an arrow, draw and anchor with no problem whatsoever. I can easily draw and anchor with an arrow if I don't intend to shoot. But when I am shooting, I tend to fall to pieces.

I've got it under control now, mostly. The problem still raises it's ugly head sometimes though.

What has helped me most was forgetting about messing with my draw length and getting a light draw weight bow to practice with. One that's very easy to draw to anchor. You have to get the feel of a good anchor position grooved into your subconscious. And I constantly have to work on drawing to anchor and holding for a 3-count before releasing to keep that groove. Another thing I do is work at my point on distance. If my arrows hit short, I know I didn't hit my anchor.