Small stomach?

[Heyimbrit]

So I've had Hoss for about a year and a half now and I've noticed that he's never really eaten big portions of food. He's a fairly big boy and he keeps weight on but doesn't eat very much. I offer lots of his favorite greens every day and bugs occasionally too. My smaller female eats easily twice as much as he does. Could he have a smaller stomach or could he have some other issues I don't know about?