Determining turned shoulder plane.

[DDL]

For a given shoulder turn, how do I determine , without benefit of an instructor, or a mirror at the driving range or golf course,where to place my hands to be on the turned shoulder plane? From the down the line view, the hands, right shoulder and ball should be in a straight line. For a flatter shoulder turn, the hands should be farther behind the head, I assume. Don't know how to check for this on my own.