A ULR flight has 2 captains and two F/O's. Team A and Team B.
Team A outbound captain claims 100% of the time to JFK, whilst the Team B Captain only gets 50% to JFK of the time for his logbook.
On the return flight, the rolls are reversed and Team B Captain now gets 100% of the flight time whilst Team A Captain only get 50%. The same applies to the first officers.. Now you get 100%+50% which equals to 75% of the entire journey.
Now that there is one captain and two F/O's, it could be said that the relief F/O might not be entitled to claim 100% of the flight time, but the Captain surely would, even if in the bunk. This means before, 15 hours to JFK and 7 hours back (logged time) amounts to 22 hours logged of a 29 hour flight, where as now that captain will now claim the complete 29 hours round trip.