So I just took some pictures of both Hunter's and Sam's adobes.
Sam is in a 40X30 cage, and he utilizes each and every square inch of it.
Hunter is in a 36X28 cage. Both cages are A&E. In the afternoons they do a switcheroo after having been out for about 2 hours. I put Sam in Hunter's cage for a few hours and vice versa.
Have a bird that doesn't use it's entire cage? Take out their big ol' food dish! Instead, place several smaller dishes (up to 6 dishes) around the cage and put a small amount of food in each dish. Likewise, you can put a foraging toy in these locations to encourage your zon to not only interact with his environment but to work for his food!