The Phlogiston

==== Wouldn't the Phlogistion be better thought of as some sort of "hyperspace", a layer to the Prime Material, or even a Transitive Plane that shortens travel time (like the Plane of Shadow), instead of merely part of the Prime Material? ====

The latter didn't, but yes, some people have speculated that the phlogiston should be seen as a Transitive Plane. I see it as a component of the Material Plane.