strato911 is correct.

The phenomena is called reflective sum and difference.

If the radio signal bounces off a large metal object it may create a secondary signal that is delayed in time.

If it reaches the receiver delayed and 180 degrees out of phase, it effectively cancels the signal. Reaching it in phase, it becomes additive.

Reflective difference is subject to frequency, soil saturation (yes), size of metal building relative to the frequency being acted upon, transmitters elevation and distance between the reflected signal and the receiver and receivers vertical height.

The difference between a hit (difference) and nothing (sum or none) can be a matter of inches. That may be why some get a hit and in the "general" area and others do not. It must be exact, horizontally and vertically. Also the pilot's height will change the reflection angle and thus the area where the "difference" appears.

Kinda black magic, but it happens more often than people think.