Originally Posted by
RecoveringYuppy
The "specialized version" they appear to be applying would be the mass divided by the volume of a sphere using the formula taught in elementary school (such school's typically located outside of black holes).
Alright. That's rather specialized because, as I've said, that formula has absolutely nothing to do with the spatial volume of the region enclosed by the horizon. It may give an empirically interesting measurement (in fact it's just a rescaling of surface area), but it is not the volume in any physically meaningful sense.