According to some golf myths such a position on the top is often being called erroneously "flat". Upright two-planish backswings never give such a possibility since the lead shoulder joint alone is too weak (in the sense - too unsecure) a connection with the upper body to guarantee a simultaneous work. Here we can use the word "upright" because the square relation between lead arm and the spine has been destroyed.
Another popular myth is that the plane height should be dependent on a golfer's height. It is just absurd since what eventually matter are body proportions - but we can even forget about it if we assume that the proportions between well-fitted clubs and a golfer's body are stable in the macroscale. There are really no arguments to think otherwise.
Today's golf instruction does not often understand biokinetics and sometimes find ridiculous arguments against low plane golfers while the truth is that the vast majority of the best ballstrikers in history of golf were never upright players. And even if some of them might have been, they were capable to shift back beautifully to the low plane during the downswing (vide: the EEP concept). However, this procedure is just a waste of kinetic force and one does not need to be a genius to state that the best scenario is when necessary plane shifts are as small as possible - from elbow plane to the shoulder plane at the top and to the elbow plane as soon as possible in the downswing (where the rear forearm becomes perpendicular to the core).
Mr.Hogan was right again with imagining the swing plane being not higher than the pane of glass resting at his shoulders. Too bad many people do not understand his intentions...:
And here is the video that visualizes the concept:
