Honestly this debate is old and it should be apparent to most that it'll never come to any definitive conclusion as people have different opinions in regards to what the minimum tank size is for a fish. Also it should be stated that those who throw definitive answers out there should realize that no matter how experienced you are without the benefit of a degree in fish psychology your statements are little more than opinion rather than fact. That's not to say in your consideration of your animal you should go as small as possible with their enclosure it's just that some of these quotes of 1000 gallons or more for 24 inch fish shouldn't be taken as rules nor should people look down on others who don't provide their fish with such enclosures nor should their be a debate about it. In a thread like this one should simply state their opinion and perhaps the reasons why and leave it at that.
The closest answer that borders on fact are the ones that only take into consideration the minimum size necessary to keep an animal healthy. Seeing as fish happiness/comfort is not a subject anyone is really versed in or has proof either for or against except in rare instances it's not a feasible argument for all fish. So stating things like the fish only has 5 inches to turn as a negative here is based on an assumption about the animals level of comfort whose reason for the assumption on comfort level isn't even explained. Seeing as animals are less evolved and probably have less complex needs in regards to wants regarding comfort it's usually not the case except in the rare instances that a fish actually shows you. Examples include Leiarius marmoratus who will let you know he doesn't like the size of his tank quite obviously. Marmoratus won't eat, will dash about suddenly, hide a lot, become lethargic, get sick easily etc,etc.... all because his whiskers are touching both sides of the tank at the same time giving him the impression he is trapped. There are other examples of visible signs of discomfort in certain fish so we can assume almost on the level of fact that they need a larger tank. What signs are those who recommend larger tanks seeing that give them the impression that the Dats are less comfortable in the discussed setting? Mind you 5 inches seems small to us but to a 24 inch fish that's a space of approx. 20% of his overall size, so while it may not be ideal it may not be as bad as it's being made out to be.
Your best bet is to always let your fish tell you if they're okay with their environment. If the fish is cramped he'll act stressed, won't be as interested in eating, become lethargic, stunted growth, sudden unexplained dashes, get sick often etc. So always base your tank requirements on what size you need to keep your fish healthy and let the fish tell you if more is required. That's my humble opinion.