I don't want to be the only one giving you advice here - hopefully some of the others will chime in as well to put your mind at rest.
Like I said in my earlier post, the best place to put the bulb (and the place where probably 90% of keepers put it) is on top of the cage, alongside the basking bulb.
What you want to create is a UV gradient. There must be different levels of UV throughout the cage. There should be a spot where it can obtain good exposure to UV and bask at the same time (just like sitting outside in the sun), and also a place where it can get UV exposure without getting hot (like in nature when it sits in the dappled light of the tree canopy - not directly basking, but still getting UV penetration). Finally, there should be a spot where it can hide from UV - like lower down in the cage (just like it would retreat down lower into the tree canopy to shade itself).
That's why placing it lengthways across the top is usually the best arrangement. The basking bulb should be off to one side of the top of the cage, but next to the UV - so there will be a combo basking/UV spot, and then on the other side of the cage away from the basking lamp it will be cooler but still have UV. And since UV only penetrates effectively down to about 12-18 inches, and decreasing in strength (depending on the bulb used), there will be places lower down in the cage where the cham can escape the UV rays.
You do need to ensure that there is a clearing in the vegetation in your cage, in the 3-6 inch space between the top of the cage (where the UV bulb is) and the topmost perch where your cham would spend its time basking. If the output of the bulb was obstructed, the cham wouldn't be able to get the full benefit of the UV bulb.
Also, make sure that the UV bulb isn't in one of those fixtures that has any glass or plastic covering the bulb (like some aquarium fixtures). The UVB frequency your cham needs doesn't pass through regular glass or plastic.
The only time I've heard of people putting UV down the side of the cage for any good reason is in really huge (tall) cages where the UV penetration from the top is very limited. But like I said in my earlier post, I don't like it there because it falls into the chameleons eyeline more than it would on the top. If you have read about the conjunctivitis issues caused recently by compact flourescent bulbs, it makes me wary of spending too much time staring into UV bulbs (even the safer tube ones). And mostly, I just think it would be irritating to the chams - it might even affect their hunting ability (next time try playing darts with a light shining back in your face from above the dart board).