Continuing to use the city of Boston as the example: You have stated that it is one diocese. Are all the orthodox churches within Boston of that one diocese? Are they considered satellites, extensions, or separate churches? (Not an argumentative question, but an information seeking question.)
We have an anomolous situation here in No. America. Canonically, all Orthodox Churches in a diocese or metropolis should be part of one diocese/metropolis under one hierarch. The situation here because of immigration is uncanonical with various ethnic churches have their own overlapping dioceses. All of the Greek Orthodox parishes in Boston (and virtually all the rest of New England) are part of the Metropolis (diocese) Of Boston, the Russian ones are part of a Russian diocese, the Antiochians an Antiochian one, the Serbs another etc. etc. Each one, however, represents the fullness of The Church and the bishops/metropolitans are all in communion with each other. The proper canonical set up is one bishop per geographical area. We might get there someday.