Um, that's possible on the FE too. No matter how many times you fly west from California and travel around the earth, it will take you roughly the same amount of time, each time.
Maybe your just not paying attention here, or maybe I just wasn't clear on this, but I thought I was.
Part 1
What happens when you leave from Texas?
Now try it from South America?
Austrailia?
North Pole?
Part 2
And we said "straight line" Not straight east, or straight west. Straight ahead as in whatever direction you are pointing in you do not turn or deviate from. If the gps/compasses are deceiving you then some of these trips are going to take a lot longer than others.
Using this method. On a round earth, all trips in a straight line back to the same point should be approximately the same length if you take into account headwinds, tailwinds, and the slight off round shape of the earth.
On a flat earth, some trips will be miraculously short, and others will be horribly long. Or you'll fly straight off the edge of the world.