the "gallons per frog" numbers are just basically guidelines. most likely because gallons are such a common term, and has been around long before the current new, high tech vivariums. if you are going for a dart that is more terrestrial, then obviously, you would want a shorter tank, with more floor space. for a dart that is more aboreal, like Leucomelas, then you could use a taller tank. that's not to say you cannot use a tall tank for ground dwellers, just keep in mind that everything above a few inches is for you to look at seriously, the best thing you can do is use common sense and good judgement. please remember that even though darts are small, they need a lot of room. and good for you for doing research and asking question before buying the frogs