First of all you can pick any airport, They relaxed their rule of 3 airlines 6 flights a day since the RTA merger since RTA allowed you to live anywhere as long as the airport had at least 3 flights per day, that still stands, I commute from an airport served by only 1 airline but it has 6 flights per day to ATL only
If you say live in DAL and make CLE your Domicile, you only have to get to CLE if your rotation starts there, you are on your own , but remember, you have to be in CLE by 0300 local the night before your rotation starts, while if you claim DAL as your domicile, then they airline you on day 1 of day 8, you would loose one day if you had to commute to CLE on your own, but they will put you up in a hotel, you just have to get to CLE, and you get $400 tax free dollars per month, now if you end up in CLE on your last day the same thing go's you have to find your own way home, but in your example, if you ended up in BOS, they are responsible for getting you home to Dallas, even if you ended up in Akron or some other place close by, they still have the responsibility to get you home, the only time you have to get home on your own is if you end up in Cleveland.