You are correct in your understanding of how they operate. Should the available half of a unit get dispatched as a single provider, fireboard will back them up with the next nearest full unit if one is available. There are also cases where two single medics will be dispatched or where a single medic and one of the supervisors (ALS ##) will be paired up to ensure two medics are on the run. The single responder will recall the backup if/when they determine it isn't needed.
You may also notice that when only a single medic is required for transport to Christiana Hospital from the southern end of the county (usually Medic 5 out of Middletown) the other half doesn't always follow the BLS all the way up to Christiana. They move up and stage at fire station 4 (Odessa) to keep an ALS provider available in that part of the county. When they do this the BLS usually gives the half that treated a ride back to station 4. ALS coverage is pretty light down there. Medic 5 is out of Middletown, and when they're tied up the next nearest unit is Medic 6 out of EMS station 6 in Glasgow from the 40/896 area.
I'm not sure where you are located, but if you're anywhere near the area you could grab one of the analog UHF patches. 453.900 is usually a good one, I've carried that through Cumberland, Gloucester, and Salem counties in NJ and down into MD.