I don't know.
It's not like Bas (or Vitor or Krystof) fight completely squared off. They do have a lead leg, but not so far out or so "linear" as many other mma fighters.
In fact, i don't think Vitor uses that stance at all...
I think the biggest difference in Bas's stance, is not on the way he places his feet, but his hands. His feet obviously will transition from one position to another, depending on what he's doing punching, kicking, defending a takedown - but he pretty much alwyas seemed to keep his hands a bit lower and out.
From my understanding, he does that because it because it gives "weird angles" to his punches and makes them harder to see coming, avoid, or block. And by keeping his hands lower, he can defend takedowns better (your hands are closer to defend your legs/get underhooks, etc).
Fedor used his hands on a lower stance than usual against Nogueira in their third fight, to avoid the takedowns, but his footwork was the usual.