That's a complex question. The astral is the plane where most of our human thoughts and emotions exist, and so the subnatural realm contacts us through the lower astral, just as the supernatural realm contacts us through the upper astral. The theory, though, is that the subnatural -- like the supernatural -- is entirely outside of those planes that human beings can experience directly. The subnatural is denser, more restricting, more limited than the world we experience with our senses, just as the supernatural world is less dense, less restricted, less limiting than the highest and least material things we human beings can perceive.