Yoda - you are correct.
I was incorrect to state that the left arm flying wedge is on-plane. I should have stated that the back of the left hand is on-plane because it is the only part of the left arm that approximates the inclined plane.
Consider this composite photo of Stuart Appleby.
His clubshaft is on-plane at the top of his backswing, which means that the flat left wrist and right palm are alongside, and
parallel to the inclined plane. However, the left arm is angled slightly off-plane in the direction of the left shoulder socket.
Yoda - this issue made me think of another question, which I have now added.
If a golfer has flexible wrists, and he can bend his right wrist back to 90 degrees at the end-backswing position so that he can get his right forearm angled closer to 90 degrees relative to the clubshaft at the end-backswing position, is that a disadvantage? In other words, I can understand the right forearm flying wedge acting as a supporting strut to the left arm flying wedge at the end-backswing position, but I was wondering whether it is disadvantageous to allow the right wrist to bend back fully by the end of the backswing - thereby altering the angular relationship between the right forearm and the left arm flying wedge?
Jeff.