We had problems with that type of crate when we first got Wilson. Had the large one just like you do. Wilson constantly panted during the night and was hot. We even got a fan and when he waked up during the wee hours of the night panting we'd turn the fan on and that did the trick. Turned out it lack of air circulation and when I got him a large open crate like your small one the panting problem was instantly solved. I think they also feel closed in, shelted in a way.