[ejhong]

As you noted, your head drops down dramatically at the start of your downswing. It looks like it is dropping up to 6 inches. If you didn't have this move you would miss the ball completely. You do a great job of compensating with this move though. Much better to drop at the start of the downswing than later on in the stroke.

IMO you are standing as far as possible from the ball at address while still being able to physically sole the club behind the ball. This is because you are using mid-body high hands with an extended left arm. No other position could get you further from the ball. At actual impact, your radius is much shorter because the hands are ahead, your left shoulder is higher and back, and your left wrist is flat. Your head and shoulders need to be much closer to the ball at setup. I believe there are various ways to do this: i) Keep the high hands but bend your left elbow until you are close enough. Extensor will snap left arm longer and taut as you start backswing ii) Lower your hands so that you can get closer. Many pros look this way. You will need a plane shift at some point in your swing. iii) Setup at impact fix with your hands ahead and left shoulder higher instead of at mid-body.

BTW - I may have no idea what I am talking about because I am pretty terrible at golf. However, I believe I suffered from having my head and shoulders too far from the ball for a long time. What's different though is my ability to compensate was much worse than yours. Rather than dropping at the start of the downswing or during the backswing, I would do my best to keep my head steady till the last possible minute. Then my subconscious would kick in at the last minute telling me I would miss the ball. The result would be a huge terrible flipping of the hands (which adds radius) or a jerky dipping of the right shoulder and head down just before impact causing a loss of balance, or both at the same time.

IMO - standing too far from the ball is a major cause of flipping. This is also why my practice swing looked so great but my actual shot was completely terrible. There was no subconscious kicking in during the practice swing telling me that I would miss the ball and pulling out compensations. Ball position relative to my head and shoulders at address is critical for me - I don't have good enough hand eye coordination to compensate for a bad position so I need to get it perfect before I start the stroke.