White's Dumpy juvenile very bony & likes to burrow???

[busytiredmom4]

I'm a little concerned about a couple things with my White's Dumpy tree frog. When I bought him a couple months ago, they said he was a juvenile. My concern is that (1) he looks like Schmiegel from Lord of the Rings-very bony. He's grown since I bought him, but his lower body is very bony and he's got these 2 bones on top of his back (towards his legs) that stick out. Then towards the vent, it's extremely narrow, almost like he's a triangular shape. The pet store guy said he's most likely bony because he's a baby and doesn't have much fat on him yet. He suggested feeding mealworms to increase his fat intake, all while keeping in mind the chitin that can cause bowel problems.

My 2nd concern is that he does not stick to the glass or climb like tree frogs are supposed to. When I bought him at pet store, he was always on the glass, but all he does here is burrow usually completely or he'll just lay in his own corner. I have lots of things for his to climb on, vines, etc. It's not too cold or too hot here but the pet store owner thinks it's just really comfortable on the ground. I admit I do have a lot of substrate in the terrarium (bottom layer of coconut husk and a top layer of sphagum peat moss. I have 2 other tree frogs in same tank and they are always in their little tree. They never burrow. I've never seen this. Even my toads (in another tank) don't really burrow much and they're supposed to by nature.

Dumpy is very friendly, isn't bothered by much, very mellow, eats fine, gets along with other 2 small tree frogs fine. Also, there's times where I don't see him come out for a few days. I read that they have a different kind of skin that controls their body temp so they can burrow for the moisture. I mist lightly once a day and I feed crickets, mealworms, flies, and other random bugs every other day and I make sure to watch them eat so I know each of them are getting their fair share.

Could it be that he's just shy and just prefers the substrate to clinging on the glass?

Should I reconsider the amount of substrate I use?

Should I feed him more often? (He's 3 inches long snout to vent and is a juvenile)

Is my tank too small? I know I need a bigger tank, and I will be upgrading in a couple weeks (started out with tiny Pacific Chorus frog and quickly added 2 more after that) It's a 5.5 gallon glass with Dumpy, a green tree frog and a Pacific chorus frog. The other 2 just hang out all day on the leaves (usually the same leaf) of a plant so in a way, there's still plenty of room for Dumpy.

I've attached pics of him on my lap showing how bony he is. Otherwise, he looks great. Clear eyes, healthy appetite, non-aggresive, no weird skin markings, etc. Please help! I have 3 tree frogs and 4 toads and I've never had a major concern with any of them. Any advice would help. Thanks!