You want to mimic nature as much as possible, and most chams bask earlier in the day when the sun is somewhat high in the sky but still coming down at an angle. You will notice that a 45 degree angle is probably the best setup for basking lights. Your cham should have a nice horizontal perch to which it can sit on and angle his flat side towards the 45 degree angle of the light.
I do know that some hard core people have setup 3 basking spot lamps at 3 different angles, and they have them setup on timers to really mimic the sunrise, midday, and sunset angle of the rays. I think thats overdoing it and unnecessary. But hey, whatever works...
Nate