Can somebody clarify why Avalon does not respond on Stone Harbor

Avalon / Stone Harbor - Can somebody clarify why Avalon does not respond on Stone Harbor box assignments? Don't tell me, "Drive over to their firehouse and find out." I am asking because that makes no sense. The location of the firehouse is supposed to be correlated to the response area. If volunteers are responding from off of the island, they are members of the wrong firehouse.