Purely my opinion, I can't tell the difference between closeness of the vocals on both(Got kinda curious myself).
If anything, it's just different. (Or maybe I am not that sensitive to the difference. I am using a female vocal, JPOP/GAME tragic song for comparison btw)
To me, the separation of 6xx might have caused the vocals to sound further for some, while the thickness of the 4xx might have "blocked"(maybe) out the sound to make it feel further for some others too.
Finally for me, that thickness i mentioned in 4xx might have made the vocals somewhat slightly stronger.(maybe not closer, but louder in some sense.)
PS: Sorry I am just terrible at audio terminologies.