One thing nobody seems to have included in their calculations (i didn't back read everything) is time, wasted time in particular. Every one of those J1's is going to need at least 2 extra days to get to a refueling sight, whether it be a high-port or gas giant, and then back to a safe jump limit. Add a day perhaps, if it's a down-port. Add time looking for new passengers and cargo. Fuel has already been discussed, but that's 2-3 extra days life support per parsec.
Sure the J6 ship has to pay those costs too, but he it can do the round trip 3 times, in the same period, assuming equal M-drives for inter-system.