Relative "badness" of interference is the same at 200 meters (hangflywer stated direct line of sight to base station antennna) or at a significant distance, 20km would result in 40db Rx level difference.
You are implying, as I read it, that at 20km from the base transmitter, the signal is still readable and the apparent noise has reduced relatively by -40dB?
Are we looking at some form of cross modulation, which includes a noise component?