The cage looks great by our standards, but snakes like to feel snug for safety from predators. You might try something with the large hide that you want
him to use. First off, the doorway seems too large & open, & presumably the interior has the same open feel compared to his small pyramid. So take some
paper with texture that won't squash down (like a brown paper bag) and crumple several pieces of it...put some inside the large cave & also stick one in the
doorway, so it blocks it partway. Then see if he'll go in & stay there?
Snake don't read "House Beautiful"...they don't like high beam ceilings & dramatic entryways...they only care if it feels right.