Moses is presented a lot differently given his importance and is more traditional --  which means in a more Iconic –  more pre-Renaissance -- pre-Perspective sort of way. But he is the only Prophet that is a relief -- and that makes him, of course,  stand out. This dynamic of two-dimensional V. three-dimensional iconology really POPS when you see it stand alone among the inverse dynamic of “High Renaissance" (twisted animated bodies on flat canvas) of the rest of the Frieze.

Unfortunately, this visual effect really doesn't translate in photos.

But what is Sargent driving at with the wings? The New York Time’s article (December 7, 1913) which talks about Sargent following Michelangelo’s example in treating the Moses “conventionally” led me to this:

Michelangelo in Juxtaposition: