Whilst this is a primarily LH operation, you cannot work too hard.
STN-EWR-STN is basically 15+ hours and 3 days work.
Lets assume 5 EWR/BOS pm = 75-78 hours (O/T paid after 50 hours)
and 15 days work
There are some short haul flights (very sensibly upping the daily utilisation) out of BHX and STN, add a few of those and we get 18 days work, and 40 hours O/T @ £90 hour =£3600 and 12 days off pm.
Whilst not perfect, it is pretty good.