How far away from the basking dock should I put my heat lamp.?

I have an RES turtle, and I just got a new basking dock. I used to just use a rock, but this new dock kind of floats on top of the water. I'm not sure how many watts it is. The box just specified it as a "basking lamp." Anyways, is 5 1/2 inches enough space? I don't want to cook the little guy.