Hmm... I don't necessarily think that just because he had a dominant ride that there's no way that he couldn't have been even faster in another scenario, or that winning a world championship means he exercised INFALLIBLE judgement with his setup, but even if he did, speculating on position changes tends to be fun and interesting, so...

If he was a person who posted pictures of himself on slowtwitch and asked for help in eeking out another aero gain, I'd probably tell him to try to scoot his seat forward a little bit and then pull out a spacer or two to get a little bit lower. That certainly seems like it would make his position look a little bit more like Dumoulin's and Martin's old position (at his peak). If he asked you for hints on what you thought could get him a bit more aero, what would you tell him? I imagine that with all the data you've collected you have much better instincts and insights than I do.