paging cmays or anyone else who may know something about it

I have been looking into movements of the body and how it relates to the golf swing. Now in relations to the shoulders I noticed something the other day in playing with plane lasers.
let me back up a litle
my posture has not been very good, not golf wise but in general. That is something I am working on. My shoulders are rounded forward, I am working on getting my shoulders back and standing more upright. Well in the golf set up I round my shoulders, now this is different then rounding my upper back.. The shouders can be drawn on the back but it still be rounded.

so to the point, when working with the plane lasers if I set up as I used to, the lasers would go about 12-16 inches outside the ball, way off plane. then I would adjust the shoulders on the back and for some reason, I got right on plane, within 2 inches. SO I thought it may be fluke so I just went back and forth while taking practice swing at full speed and sure enough, alternating it and doing it around ten times each way it was the same results. rounded shoulders, way off plane, shoulders more drawn on the back, on plane. No other swing thought or adjustment
any Ideas or insight on this G1 or anyone?
thanks

hi
lee trevino use to do something the same, he had a outside to in backswing and his hips would slid and put his his swing on an inside to out downswing and he did it time after time, and is still in the top 5 for ball striking.
bill