Interesting, to say the least. I maybe don't know how this works then. I was under the impression that the screen I was looking at was giving me the frequencies in use on that particular tower, not neighbor sites. Even then, there's another site between Sanborn and Sioux City -- Le Mars. Not really sure now what I was looking at.
I am not familiar with the discovery mode for the HP. Could it be showing neighboring control channels? I use unitrunker and depending which screen you look at, it with show all the known channels in the network or another it shows the peer sites with the control sites, Then the main screen just shows the channels for the site with the traffic that is going out over that site.