I wish you could post a video of yourself playing from different angles because there are a few inconsistencies in what you're describing. For example: You say your arm moves off-line during the stroke, but at address, your elbow is not off-line. Your stance may be a little off but most amateur players stances are a little off. If it was significantly off, your elbow would not be in a good position at address. I doubt that what's causing this is your stance. That's why I wish you could post some videos. I'm sure we'd be able to help you figure out what's really going on and why your arm is moving off-line during your stroke.Thanks, Fran. Sorry to hijack the thread a little, but as you describe it, it's not chicken-wing; it's steering. But in my case, it was not caused by trusting my setup, or anxiety. I simply had no way of ensuring my elbow doesn't come out the way my stance was. I tried and tried to envision my forearm coming straight in my foreswing but no matter how much I concentrated on it, it would come out about 1.5 - 2".
The only way I reduced it, and seem to have eliminated it, was to make a MUCH straighter line between my bridge hand, my left shoulder, my head, and my grip shoulder, elbow, and hand. Previous iterations of my stance had my shoulders more square to the shot than the aforementioned pro Shane (I did a side-by-side comparison using a video frame of my own stance and Shane's and noticed the difference in shoulder alignment).
The only problem I have now is with my neck, as I had mentioned, I broke my neck in 2010, and getting my face square to the shot while my shoulders are in line with the shot is not easy for me, and after 30-45 minutes becomes painful (the C5/C6 disk starts to encroach on the nerve going to my left arm - which is why, when I fractured my C4 vertebra, my left shoulder, arm, and hand were paralyzed, and didn't fully recover for three months while my C5/C6 disc fully resorbed).
So I am continuing to work through adjusting aiming with sometimes less-than-optimal head position. It's an ongoing process, honing my foot placement (it's a little more open than Wilson's "orthodox" stance) yet still having shoulders lined up such that I deliver the stroke without my elbow going right or dropping. I notice it's much straighter when I really focus on keeping my elbow high, and not dropping it - AT ALL.
EDIT: (Sorry, this is mostly a repeat of what I said in post #13. )
And BTW, I don't think this is a hijack. It's very much in line with what the OP posted. Same subject matter.