Of course, at night all get worse.
(And today, 5 mV/m is not adequate in many areas of today's cities)
That's true. Even the ITU has established, given the increase in terrestrial noise, that 10mVm is the minimum field strength for reliable reception of AM signals.
1090 has pretty significant designed nighttime nulls to the Southeast and South. One can sit on a hill in Des Moines and see the tower lights for 1090/770, but not be able to hear the station. That null includes areas like Kent and Maple Valley at night.
It's one thing carrying a junior hockey league, quite another a professional NHL team.