For what it's worth, in all my roughly 60 years as a shortwave listener I've never heard AIR even once, no matter how hard I've tried. During some of the earlier years I was living at lower latitudes (New Jersey), with better antennas and under better propagation conditions, too. DX was great back then. Even R. Peking was booming in, and at that time it was direct from China, not via a relay. For some strange reason AIR was one of the few exceptions.
I used to hear it nearly every morning in 2002-2003, when conditions were better. Generally there would be an AIR outlet behind one of the Chinese stations on either 49, 41, or 31 meters early in the AM. This happened most mornings during that winter. Once I heard the AIR outlet broadcasting from Chennai (Madras), in the 31 meter band, clear as day. Very odd. There were great conditions that season.
More recently, I was able to hear the AIR outlet on either 31 or 25 meters (can't remember which) on good nights. And I live in a hole. But then, the Cascade Mountain range is to my east, so it's not in the way of things Asian.
As for your comment on hearing more on the Canadian Prairies, I would think that the flatter terrain, combined with the elevation would have been a factor in SW reception.