[ To his credit, he catches himself before launching into an explanation of how a human-sized thing can have its parts rearranged to fit into a box-shaped thing. ]

It's best to disregard commonly understood wisdom about the conservation of mass when dealing with stands. He's not really made up of atoms, so many of the rules as we understand them don't apply to him. He'll reduce his total mass if he needs to fit inside someone smaller than he is.

[ Something. He probably meant something. Probably. ]

The smallest he's managed to become was around the size of a red blood cell.