So I've been thinking about this subject for a while now, and hopefully a few pictures will help illustrate my thoughts.
When i think of deep hands, i think of Charlie Wi. His hands are on the elbow plane, shoulders have turned at a right angle to his spine and his arms have not lifted off his body. Thus, he appears to have a compact backswing.
I think i have a very solid backswing too. I do the many of the same things he does during the backswing, my left shoulder goes down, hands in, arms don't lift off the ribcage. However i noticed that by the time my shoulders have turned 90 degrees, my arms are still at A3 rather than where they should be at A4. My right arm is folded at about 90 degrees, but PA 4 is not loaded across my chest.
To get any further height and depth into my backswing and to get the shaft to where A4 should b, I over rotate my shoulders to 110, even 120 degrees.