Once you cross county borders, you might be changing dispatch centers. Are you accounting for the dispatch delays with inter-county communications? County A has to dispatch the appropriate units in their county, and also call County B and request that they dispatch unit X for the call. Then County B needs to dispatch that unit. Likewise, all updates between the 911 caller, other responding units, and Unit X need to go through County, unless Unit X has a radio to communicate with County A.
We've been discussing this locally, because part of our territory has a 2nd due medic that is coming from the next county over. There is a move to change the dispatch cards AWAY from this unit because they have limited ability to talk with our BLS units and County. Also, in our case, there are other ALS units in county that might actually have shorter response times.