Yeah in 2.2 it does show up in a tip, that building more radar sites increases its range. Nice to know that it does not do this, as I too was wondering why with more sites the range stayed the same. I think I've read "somewhere", that there is some tech to be researched at some point to allow the building of "advanced radar sites". If that's true, and my memory is not misguiding me, I assume that it must be one of the multitude of things in the TODO list.