1. They are fish
2. They are not steel or plastic, they are capable of turning
Personally I would not put a 20 inch fish in a tank that is 20 inches wide (TBH would also depend on the length of the tank)
10+ years ago when I first joined MFK I can recall the Oscar in a 55gallon or 75 gallon debate, now I read posts stating that an Oscar for example would be too big for a 100 gallon tank, LOL
10+ years ago Oscars were listed at peaking at 14 inches, the other day someone tried to tell me Oscars can get 17 inches, I was like WTF?!! I don't know what is going on, did these fish after 10 years all of a sudden inherit some special powers that enable them to get bigger than they were 10 years ago.
I guess the point I am trying to make is, while I agree the bigger the better, judging by what size tank people recommend for an Oscar for example, it just seems that why should we even be able to keep fish if we have them cramped in a glass cage anyways?