I moved to Greensboro, NC last summer and discovered four things: 1) Blackout Restrictions apply here in a state that has no MLB team; 2) my "home team" is the Washington Nationals, which is 250 road miles away; 3) If the Nationals are playing, I am blacked out everywhere--cable, online, you name it--from watching the Sox play; 4) if the Nationals aren't playing but the Atlanta Braves are, I'm still blacked out from Sox games.
I did some cursory reading and discovered that regional networks--I think that's the term--provide about $2.1B in annual income to MLB. Because of that, they insist that the entire country be divided up among them. There are no gaps. One article pointed out that five different MLB franchises have some claim on the residents of Iowa, which of course also has no MLB team.
As for the Sox, only New Englanders can get Sox games live, and I think small parts of CT and RI belong to the Yankees (or Mets).
Feel free to contradict or elaborate on the above.