Not only that, but the way that the signal is transferred comes into play.
Ever go out driving and find your town's radio station transmission tower? ever noticed how high the antenna is? That's because radio stations, cell towers, tv stations, etc. have to have line of sight with everything that it is broadcasting to, so it is generally seated where it can get the highest range for broadcast. In Las Vegas for example, that is on Black Mountain in Henderson, which is visible by the entire city. Either way, the transmission is done in a pyramid shape, where it goes from the top down.
Flip that upside down for ATC. the range is absolute at the transmitter but spreads out the further up and away you are from the transmitter. This is why a plane could contact the tower some 15 - 18 miles out on final, and you couldn't hear the tower unless you were about a mile or two from the airport.
Think of ATC and its range like a waffle cone. The further up and away it gets, the further out the transmissions can be heard.