I think this discussion is getting all caught up in semantics, much like the discussion over leggings/pants/footless rights can get. Definitions are more important than buzzwords, and sometimes even then we have different pictures in our heads.
Volume, to me, indicates a more structured garment that is oversized. It literally creates volume, or the look that something is bigger than what it is. Oversized can be high volume or low volume. Fluid fit is all about fabric and movement, and a garment can be oversized and fluid OR oversized and have volume, but not both in my head. To give a more vivid description, Stevie Nicks was all about fluid, while David Byrne from Talking Heads was all about volume, even though both likely wore garments that were oversized. I may be totally off the mark, but that's how my head sorts the terms.
As for what my eye has adjusted to, I still prefer higher volume looks with another garment that is slimmer. Fluid fits or oversized and fluid garments can work to me with other fluid garments.