I live in an area where I should be able to get good signal on 5 OTA HD stations. I have an external Winegard Square Shooter that's aimed at the two towers shared by those 5 stations. The SS signal is split in the basement and fed via diplexer to two outlets upstairs. On my HR10, I get 60-70% signal on 3 of those stations and 0% on the other two. On the HR20, I get 90+% strength on all 5. Is there really that much difference in the OTA tuners of these two units, or is it more likely that there's something amiss with the cabling between my cable point and the HR10?