What is a characteristic of skywave signals arriving at your location by both short-path and long-path propagation?
Why Radio waves travel about 300,000 km per second, so a trip around the world takes roughly 0.14 second. When the same signal reaches you both the short way and the long way around the Earth, the long-path copy arrives many tens of milliseconds later, which the ear hears as a hollow echo or ringing on the signal. This is a classic clue that you are hearing the station on both paths at once.
Watch out The ideas about cancellation or a 3 dB boost assume the two signals arrive in phase or out of phase, but the path difference is far too large for that kind of coherent addition at audio speeds; you get a time-delayed echo, not a fixed level change.
Long way round arrives late: the signature of short plus long path is an echo, about 0.14 s around the world.