I downloaded data for several specific ADS-B receivers and given the location of the receiver I found out the maximum range for multiple receivers is around 400 km. I believe this is not due to false reporting in the messages. However, some references say the effective range of ADS-B is about 280 km. Is there any specific reason why the range in OpenSky database is larger than that?
If a receiver is on a good location and aircraft is high enough, 400km is not nothing surprising - transponder output power is strong enough to cover this distance. Not sure which references say 280km as a maximum, maybe there's a mix-up with units - should be 280NM and not 280km?