what size cage? I have 2ft X 2ft X 4 ft and I run mine in the middle diagaonally. i use a 30 inch fixture and a 24 inch bulb. When I say the middle, I mean on top of the cage but on a diagonal angle.
On top next to the basking light, so that the Cham gets both while basking. Usually as central over the cage as possible to cover as much area as possible. The basking light can be off centered and only over the basking branch.