The most important thing about the basking spot is that it should be the right temperature, and that you are monitoring that temperature regularly. The basking spot is the hottest spot in the cage and any upward fluctuations of the ambient temperature could quite easily increase the basking temperatures beyond the safe range for the cham. And temperatures that are too hot kill chameleons far quicker than temperatures that are too cool.
So that would be the second most important thing: wherever you place your basking spot, just make sure that there is a cool area somewhere else for your cham to escape to when it gets too warm.
Make sure the basking spot is not too close to the heat bulb that the chameleon can get burnt by the bulb (and never have the heat bulb INSIDE the cage). Chameleons don't seem to be able to sense themselves burning, and it is quite common for them to get burnt on the casque and spinal ridge if they're too close to the bulb.
The other thing to think about regarding the basking spot is UVB exposure. Since it will probably spend most of its time under the basking lamp, generally it is best to make sure that your basking spot is within 12 inches of the UVB bulb as well, so that the cham can get some UVB exposure when it is basking.
And then lastly, make sure there is a bit of dense vegetation near the basking spot for the cham to escape to if it feels threatened. Chams don't mind exposing themselves to the sun, but they never want to be completely exposed without anywhere to hide (obviously though, you can't put plants directly in the basking spot because the leaves of any live plants directly under the heat lamp will burn and die).
I don't think it matters whether the cham can see the feeder cup from his basking spot or not. As long as you have seen the cham eating from the feeder cup, he will know where to find it again. Only really small chams in really large cages will have problems finding their food (or in cages where free-ranged food can hide away in places that the cham can't get to).