Another solution is to mount an external yagi antenna so that only one site antenna gets gain to the scanner while other sites are attenuated. This will require getting a map of the sites, then looking at the radiation (reception) pattern of the antenna to see how you can point it to make one site come in as strong as possible in relation to the other sites.
Plot out your location and the location of all of the sites. If it looks like you can do this in your situation, you will be pleased with the results. I did it in my old home, and the results were outstanding. I went from what you got, to 95% reception. Now keep in mind, this WON'T always work. If any direction you point there is more than one site somewhat in front of the antenna, you are out of luck, as I am now in my current location in Buckeye trying to pick up the RWC signals. From my location, all sites are relatively in the same approximate direction, so I get what you get, garbled bits and pieces, which means I now just monitor nearby stuff (luckily I work right beneath a simulcast a tower and get awesome reception at my desk at work still).
On a recent trip to Mesa, I noticed that there was a sweet spot right near the big comm tower at the 60 and I think Dobson (not sure). If possible aim for that one and hopefully the other sites are off at different angles.
Good luck.