well in my set up i have the TUBE reptiglow 5.0 uvb/a output light in the back going across the entire cage....then i have my heat light in a corner above a nice branch...this gives a nice distribution of uvb/ heat areas...just remember no compact uvb lights! only tubes!
One corner is probably better, this provides a slight horizontal thermal gradient also.
Chams are notorious for climbing to the highest spot in the cage, so they should be able to do this without experiencing the max temp aswell.
If using a linear Uv tube that extends accross the cage, this will also allow your lizard to bask for uv without the heat if it chooses to do so.