[CarVac]

Longer flights have better fuel economy only in short range regimes where the BFR is definitely not a consideration.

https://commons.m.wikimedia.org/wiki/File:777-224_fuel_burn-...

Fuel economy improves at first due to reduced overhead of taxiing, takeoff, and ascent, but as you go farther the fuel consumption increases due to the need to actually carry the fuel.

[Retric]

Aircraft choice plays a role here. Airlines tend to use more efficient aircraft for longer flights.

[jryle70]

Airlines use longer range aircrafts for longer flights. That should be obvious, shouldn't it?

[Retric]

Efficiency is one way to increase range. Wingtip devices can reduce drag by inhibiting vortex formation, however they increase weight so there is a minimum flight distance before they are a net gain. https://en.wikipedia.org/wiki/Wingtip_device

There is a tradeoff of needing carry more fuel over a portion of the flight, but the aircraft also spends a higher percentage of it's fuel on flying vs taxiing etc.