The lighting behavior I just described is usually due to the iguana being too cool. You have to have a proper warm end, and a proper cool end.
IMO your cage is adequate. Iguanas are better off in a cage that is short but has a big footprint, so they can live terrestrially instead of arboreally (if that's a word).
Do I have this right? On the floor, the cage measures 10 ft in one direction, and six feet in the other direction? And it's 5 ft tall? That's just fine! You can make ramps that lead to the top of the cage that he will enjoy, even though it's not 7 ft. 6 inches tall. He can run back and forth more than in a more typical cage, giving him exercise. Sacrificing floor space to get a taller cage produces the "telephone booth" cage design, which is bad for igs.