90 gallon tanks are 48by18by25
75's are 48by16by25
I don't think two inches in depth is going to make that significantly more space for the fish. It's nice that people like to give out advice, but if you really haven't kept them and your just relying on the internet for info. That usually isn't very reliable source.(unless it is first hand information) Since I have started keeping fish almost a year ago, and being on these forums for only 3 or four months. I have come across alot of miss information. Wait for somebody to post that has actually kept one of these guys. A fish that can get 20 inches long you want them to be able to turn around so 4 or six footer with 20 inches in depth? (guess)
Remeber they grow slowly and will take up to 2 to 3 years to reach the max size and in aquarium they usually don't reach the mature size of 18 to 20 inches in captivity. I've had one for 8 months and he's only grown about 2 inches in this time. He lives on bloodworms, is very peaceful. Feeds with cory and even guppy. I have had ottos in with him from the start and I still have all 5. He much prefers his markets shrimp, bloodworms and tubifex to live fish. He's a bit lazy as a hunter. In the wild they live on daphnia and copepods.