Do you have a snug, round shaped hide that you can try? Maybe he wants to feel something all the way around him. I had a big female that preferred to curl up under a round plastic bowl, rather than the RBI hides.
I switched today large hide to middle.... We see if he can fit there... and tomorrow i will just put water bowl without water and will see is a water he need or tide hide...
1.0 Striped African House Snake "Marduk"
0.1 Striped African House Snake Ishtar
1.0 black phase Brown House Snake Seth
0.1 black phase Brown House Snake Nephthys