I mean maybe I‘m an outlier but I always use the physical buttons or knobs to control volume on my devices. I think that is by far the fastest, most exact and overall most user friendly and unobtrusive option, even when you have an agent that‘s always listening (which is a future I don‘t want). The point about being across the room is fair.

About that study: I‘m interested to read it, as it seems to contradict established literature on UX (not to mention lived experience) - do you have a link for that?