Well, there's definitely some learning required on our part as scanner hobbyists. If you've waited until after the money was spent to find out what you're getting yourself into, then, well, you get what you get.
As far as multi-site trunking, it can be a very strange animal. As was stated earlier, different sites carry different traffic, depending upon configuration and user affiliation, etc.If you're trying to receive traffic that's local to where you are, then you'll probably be successful. If you're trying to receive distant traffic, your results will likely be hit and miss. Remember, none of this was designed for scanner enthusiasts. We have to be happy with what we get and be willing to learn. I wish you well in your endeavor.
In reality things are easier now than they were when I started scanning Phoenix fire and PD. Up until the early 2000's, most PPD and PFD traffic didn't involve repeaters. Only the hot calls went on UHF repeaters and that was just PD. Most traffic was VHF, and mobile to tower was only heard by the Phoenix radio tower, scanner users very close to the patrol car or fire vehicle, or those like myself that built a tower to get my antenna up at 75' above ground. That was a serious amount of work and money, and though I could hear most transmissions, I still couldn't hear them all.
In 2019 it's pretty easy to get a small 700 MHz yagi pointed towards a site and once you get a decent signal you will hear all transmissions (unless encrypted of course). Phoenix fire medical K DEC traffic is still mostly unencrypted so you can hear almost everything. VHF analog A DEC fire ground traffic takes as much effort to monitor as it did 30 years ago though.