actually, a horizon implies flatness.
at a certain height (not sure what that is), you should literally be able to see the earth curvature, NOT a horizon.
so we need a physicist to tell us what that height would be. it requires complex physics, which is above my head.
the difference between 3000 feet and 35,000 feet is because the perspective of the horizon changes with altitude. but it's still a horizon, which implies flatness.
you're seeing a flat earth. you're not seeing a globe. but it could be because the altitude is not high enough.
the logistics part ... could be ... could have to do with finances, managing staff etc ...