Butt of the club to the ball like in baseball. Ideally at left arm parallel the shaft of the club should be pointed just behind the ball. I teach the entire down swing plane (in depth) in Golf Swing Fully Explained.
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If you come over the top, you should set up a barrier during every range session. @theswingplate makes a great, functional barrier to use. I explain this mistake and how to keep good body moves in Golf Swing Fully Explained.