Hi Nick,
No simulcast means you are not in a synchronization null. That's good, but you may still be in a spot where there is some kind of obstruction between you and the transmitter.
The tones are close together. That's good. Sometimes systems use extreme tones. That's common when Plectron tones are carried over, you can have something like 369 Hz and 2700 Hz in the same page. It's hard to equalize and one side either trails off or gets cranked so much that the other side gets distorted (neither makes for reliable activation). That's not what you have. The system should be fairly well equalized within the same tone group.
I saw you have a number of repeaters out there, each with different DPLs. I don't know for sure, but dispatch might be using a control station that switches DPLs to access the individual repeaters. DPLs might interact with the signaling, but it's not likely.
What I was getting at with the dispatch console and control of transmitter thing is analog wireline links have certain frequency attenuation characteristics. There is a thing called "high frequency roll-off" that affects very high tones (over 2000 Hz). We would have to put in "conditioned" phone lines to account for that, and they were much more expensive because they used rented equipment in between the dispatch center's. That's probably not it.
One last thing - when you are affected by not alerting, are you near a computer, wired LAN, or some other kind of unintentional emitter of radio frequency energy? What I'm getting at here is that sometimes we have electronics in our home or in our neighborhood that increases the noise around a signal and decreases a receiver's ability to hear well. I get this in my car on my VHF radio when I park in my driveway because my IT stack is next to the car. I also get noise near computers and a neighbor has a plasma TV that wipes my 440 MHz ham repeater input. Noise might be affecting you (even if the signal from the repeater you receive alerts from is good). If you shut down things one at a time, can you notice better reception?
If that's the case, no matter how many times you switch out Minitors you won't get reliable performance until the noise situation is remedied.
Does your system use simulcast? NO
What are the tone frequencies used? A 1122.5 B 1433.4
Do other people get their alerts without any problem? YES ON MINITOR V'S
Where are you in relation to your base stations? SAME TOWN
Where are you in relation to the other people who get alerts without any problems? SAME TOWN/SAME FD
Does the base drop below squelch threshold when you are walking around wherever you are not receiving alerts? NO IDEA ON THE COUNTY DISPATCH CENTER
What kind of control link does your radio system use to connect dispatch to each transmitter site? THEY ARE ON A MULTI TOWER REPEATER SYSTEM NOT SURE ON THE LINK
What kind of console system does dispatch use? NO IDEA
Do the A and B tones sound as loud when you listen to them on another receiver? YES
Are there other stations on the same frequency close by? OTHER FD ARE ON THE SAME FREQ BUT DIFFERENT TONE SET
What's the call sign of the involved system? WQRC950
A lot of these questions (but not all of them) can be answered by looking at the system configuration on the license. Those might be some of the variables involved in why something like your Minitor doesn't work consistently