US Open Champion, Sandra Palmer shows the easiest way to determine your best stance width and posture for irons and woods.  Take a 10 pound weight disc attached to a bar and center it across your chest as Sandra has in the following video.  You were given several stance widths from your body measurements.  Place the middle of one foot on the zero point and your other foot at one of the stance widths you were provided.

You will notice that when you are in your best stance width that you have minimal movement of your head.  Notice how level Sandra's and my shoulders are in our rotation.   If you are not in one of your balanced stance widths, you will have a restriction in either your backswing or downswing.  Work on a level shoulder turn in your motion drills.

Interestingly, when your stance width is in your ideal balanced position and your "Power Angle" posture is set, that angle shows up in over 15 positions at address with irons and woods.