There was some error in my maths on the first pass. Fuel Surcharge quoted is for a return journey. Originally I calculated Fuel Surcharge for round-trip against one-way fuel costs.

Analysis does assume flight are operating at 100% capacity, which is likely to be improbable.

Airlines can mix seating depending on 787-8. I got the figure 232 here: https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft