Fire Belly Toad tank Size Discussion

[Cricket1234]

I have been planning on going into keeping fire belly toads, as I had kept them in previous years, and realized people's opinion of things like diet and tank size has massively changed. One of the main things I noticed is that there are now people saying that they need 20 gallons or so, with 5 gallons more per additional frog.
In my opinion this is kind of overkill. Keep in mind that I would build my own tanks, so the 5 gallons that I would house my toads in had a larger footprint and were more lengthy and wide, while opposed to the standard ones that are higher with less floor space. Can you guys explain to me why exactly a 5 gallon is or isn't suitable? There was literally no behavioral or lifespan difference between those I kept in a 15 gallon than those that I kept in a 5.