Poseidonet is limited, and does not work well. Long ago Avellone said Enclave communications were in bad shape, and that the Rig only had contact with Vault 8? to give the all clear, which becomes Vault City, and Vault 13.
For the most part, you are looking at short range for any kind of viable communication, and ham radios.
It is also not clear if Eden or Richardson gave the order for the Enclave to go east. The FO3 gamw guide states "on orders from the President, Autumn Sr. sent to the only Enclave base with a functioning ZAX supercomputer".
But, which Prez? Was this a contigency plan for Richardson, or Eden? IMO, continental communications would be impossible following a Nuclear War, so it makes sense the order was a contingency, " in case of disaster" plan of Richardsons.
Regardless, doesn't matter much except for logic.
Next, yep we have no idea about Chicago. Pre-existed, or drop offs from Autumn. But, if Autumn stationed units there, why Chicago? Was there a base already there? It really doesn't fit in logistically, so what purpose? Who knows.
Another reason I do not think communications were good. The DC Enclave seem oblivious to the fate of Navarro. Eden seems retarded that he doesn't know if the original FEV was a success "I have to assume it was a failure, as I never heard of its success". In fact, it makes more sense to me if Autumn was sent east before the rig even blew up.
Basically, there are a lot of unknowns when dealing with Enclave. Huge gaps in timeline, with really very little info, so the rest is left up to speculation.
Now, a good writer could answer this shit, and develop a good story behind it.