Wait a week, and let him settle in some more. Are his hides low to the ground? I think I know what cave you're talking about and it's a bit high(like a tree stump?).
When he curls up inside it, he touches all sides (as far as I know the top as well).
Heres the picture of it.
It looks a bit high, but the rock is about half-inch thick give or take at the top. On the sides its thinner.