To me, I think your top position with the bar is a little far back. With the bar already being so far behind your head it will be difficult to hit a good bottom position because you are already under strain at the top.
I would like to see you just stand more comfortable with the bar more over towards your head. When in this position you will be able to hit the bottom allot better.
See - http://www.crossfit.com/exercisedemos/
See the difference between you and the demo?