Its seat type. For long haul routes, Premium Y is needed for 95-100% LF. I've noticed this with my wide and narrow body aircraft.
Given CI 100,
HD chairs run about 65-75% LF on routes with more Y demand then supply. However, the same route with another aircraft with Standard Y yields 78-85%.
This leads me to think Prem Y will allow you to reach 100% LF. Though I have not tested a perm configuration due to the reduced amount of seats you can have.
Not quite sure a widebody configured for 200 seats when typical seating is above 250 can make enough money on a route where competition runs 200% above demand...
Least, I'm not ready to make that jump