Well, turns out I'm having no trouble getting CHCH from Hamilton.

In fact 18.1 is the FIRST channel I've ever received on my Sony HDTV DVR *without* having to run a scan in advance (previously, 100% of HDTV channels would not tune in unless I've first done an antenna scan, so that it can access and cache the PSIP - it makes it hard to hunt for weak signals, however even though it won't tune in a frequency it doesn't know about the signal meter will still indicate a signal's presence).