The main concerns I would have is that it wouldn't stay in the area of the UVB as long as it should and that your ambient temperature might vary from quite warm in the basking area to quite a bit cooler in the other areas of the cage.
You don't want it stuck under the UVB light so it can't move away if it needs to though. In the wild, the UVB is "everywhere" that the light is but there is a range for the UVB lights in the cage that limits where the chameleon could sit.
BTW...this would only apply to cages kept with UVB lights not to ones kept outside all the time.
Hope I explained this clearly enough?
Personally I use cages that are longer and lower for babies so that things are more even. Just my own opinion...no scientific study to quote on this one!
If you don't want to spend money to buy another cage, why not just divide the one you have in half to make it shorter for a while?