I'm afraid I'm not real familiar with the sites in that area. My best suggestion is to get a RTL SDR dongle and decoding/logging software such as Unitrunker or DSD+ Fastlane, these programs (and several others like them) allow you to log a P25 site 24/7, after a while you can get a really good indication of what talkgroups frequently affiliate to which sites in your area etc. With Unitrunker you can even log multiple sites at once, depending on how many dongles you have and the frequency spacing between the control channels. In my experience Unitrunker v.2 (still beta) is by far the best program for logging & reviewing site data (others are better for decoding audio). In general with DTRS, you will sometimes have a site that gives you great coverage but has very little activity relative to other sites that you might still be able to monitor.
Alternatively, I would suggest running your scanner in Band search mode on 850-861 and a separate band search on 769–775, and search for any and all P25 control channels you can pick up from a particular location. I do this fairly regularly while traveling through areas I'm not real familiar with, it's the most accurate method to quickly determine what CC's you can hear from a particular area.
