I guess this is the open racket position that you are referring to in the OP? See video.
Single frame on Vimeo. Hold down the SHIFT KEY and use the ARROW KEYS.
Could it be that his hand on the throat works better with face up (open)?
He comes out of that racket position as he brings the racket down in what looks like a forearm/arm rotation.
I believe that the farther from impact a racket position is - in the take back or the follow through - the more variations might be seen in the strokes of different players. It makes understanding why the hand or racket orientation is being used more difficult and uncertain. First study how many one hand backhands use the 'open racket' orientation that you are interested in.
To get a quick look of many pictures (on any subject) -
Google:
one hand backhand take back images
To post pictures that are allowed, right click on the picture and select
"Copy Image Location". Paste into a reply using the picture icon (mountains..) at the top of the reply box.
Post illustrating how the racket is brought down after the 'open racket' orientation.
http://tt.tennis-warehouse.com/inde...tart-forward-swing.462997/page-2#post-9818922
The later posts of the above thread describe the '
credit card one hand backhand'. This is the biomechanical mechanism that I believe accelerates the forward swing at its start for the strongest one hand backhands.