Shouldn't draw too many conclusions from an informal practice session. Some of his volleys & movement are a bit sloppy here. There are plenty of videos of Roger warming up where he does not employ knee bend. In actual play, Roger may have his racket slightly skewed for his "ready" at the net. It is certainly not the "ready" shown in the 2nd image in the OP.
Roger reads the ball much better than the rest of us. He also has world class reflexes that few possess. He would not have much trouble getting his racket on the ball from any ready position. Not true for us mere mortals.
When I hit my FH volleys, my contact point is pretty much forward (nearly even with my front shoulder, not my rear shoulder). I do not have much difference, if any, between the contact point for most of my FH and BH volleys. Regardless of the CP, the limiting factor is actually how much time it takes to get the racket around and the wrist laid back for the FH.
My hand moves forward a bit as I turn to line up the ball for either a FH or BH volley. Not much wrist extension for the BH volley at all. I can quickly pivot the racket to set up for the BH -- much quicker than for the FH. This is why I advocate a neutral racket orientation for the "ready" at the net.