I monitor a large multi site system in south Florida; it's a NXDN 4800 system (It's Highland Wireless, not yet in the RR database). Each site has between 1 and 8 frequencies. It seems that all the sites come in about equally well (or poorly), even though some are closer than others.
One of the sites is a "fill-in" site with only one frequency. It's the control channel, sending out a continuous data stream until someone transmits, then it becomes a voice channel until the conversation is over. Not too surprisingly, this site gives me almost no dropouts or missed replies. It doesn't have to scan any channels, it just sits on the one frequency.
Because this site is only one frequency, most of the fleets on the system are not permitted to affiliate on this site; it has only a couple of users. So it works well for the traffic on it, but it's no good for monitoring most users.