You are referring to the reactive near field region, lambda/2pi, which is used for antenna characterization. At the lower end of human hearing (20-40 Hz, using 40) that figure is 1.36 meters. Any room larger than that -literally all of them, unless your ceiling is very low- will propagate a traveling pressure wave instead of just pressurizing.

Further, that figure isn't very helpful for fluid acoustics. Within the equivalent distance you instead would get tons of nonlinear effects, because fluid flow dominates acoustic transmission. In addition to heavily changing transducer loading, things like vorticity also start to dominate. The net effect is that near field issues arise much earlier, at more like a third of a wavelength. Still, only the very lowest audible waves and quite small rooms create non-acoustic behavior.

> once you have reflections (from, say, the ground) you have to account for that as well.

Ish. Only for quite high frequency sounds which change very quickly. Otherwise reflections tend to mostly just overlap with the primary source. For low frequency waves the distance between the microphone and your ears is much smaller than the wavelength, so you don't need to worry about multiple waves very much.