Reverb - Room dimensions

I do not believe that precise dimensions for a specific room are intended here; rather, it concerns a general context in which the sound propagation time for a specific distance (the longest in the room—see below) is used as the basis for calculating reflections.

https://valhalladsp.com/2018/07/09/reverb-101-size/

Does the Size parameter have any relationship to the physical world?
Kinda. In some cases, when the size is listed in meters, the Size parameter can be viewed as representing the longest dimension in a rectangular room. So, if the Size is at 30 meters, the virtual “room” would be a rectangle with 30 meters from front to back.

In reality, a room with a front-to-back dimension of 30 meters will almost always sound far richer than an algorithmic reverb with a Size of 30 meters. This has to do with the resonance density of the room, which is a pretty esoteric topic that I will tackle in a future blog post. Suffice it to say that higher resonance densities sound smoother, and digital algorithmic reverbs are hard pressed to achieve the resonance density of a fairly small room, to say nothing of a concert hall.