Maybe its just mine, so it won't necesarily be the same for yours, but I've always seemed to have small panthers until I'd move them to a really large enclosure. It seems as though the added excercise of roaming a larger space helps them metabolize their food better and grow at a more normal pace? Because I'd have a 9 month old panther that was still at 30g and comparable to a normal 3-4 month old. Now he's 1 year old and he's nearly trippled at around 80-something g. All seemingly due to the much larger cages, because no other variables changed (food, amount of food, lighting, temps, etc.) So I don't know if my observations have any validity, but I tend to think young chameleons would do just fine (or better?) in one of the 4x2x2 cages.
Just some thoughts.