For frogs growing up, they advice a smaller terrarium, they will be able to find the food better and will therefore grow more easily.
I tried it out to get it proven, and indeed, raising juveniles in a big setup results in smaller adults then ones of the same clutch raised in smaller tanks.

I am also puzzled since i reasoned in nature they got even more space,
looking at fish that will grow bigger as you put them in larger tanks i supposed it was just made up.
But now i'm certain of it, it's better to keep the frogs smaller 'till they are grown to semi-adults.
I tested it on some red eyed treefrog babies and the result is they are almost 0,5 inch smaller