shoulders in the golf swing

[shootin4par]

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 with the back still 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?
thanks

 

[hue]

I found your post confusing. The shoulders are not on plane in the backstroke. On the downstroke the trail shoulder SHOULD move downplane and continue to do so untill you have run out of trail arm.