That channel is named “Islandwide 2” in the radios. “Islandwide 1” is the simplex talkaround channel of it. As you see, the frequencies are licensed to Ocean Beach who hosts it for the whole island to utilize. Everyone uses “Islandwide 2” to communicate with FRES and each other. Ocean Beach has a few other repeaters at their disposal, one of which is their primary operations channel on top of using Islandwide 2 to communicate with FRES. Saltaire and Davis Park also have repeaters of their own but they aren’t used often and the range is very limited to their districts as they don’t have much height.
To answer your question, FRES only started communicating with the departments on Fire Island via Islandwide 2 in recent years. The transmitter located at the CI courthouse is for FRES to use to hit the repeater located at the Ocean Beach water tower effectively. The CI courthouse is clear line of site across the bay.
I hope this information helps you.