I know there's always a horizon line in terms of cinematography and perspective, I'm just saying we wouldn't see it the same way on Bespin since there's no ground to differentiate between the clouds. By definition, a "horizon line" is where the ground meets the sky, correct? Well, if there's no ground, how can we see a traditional horizon line?
Anyway, I don't see a problem with that shot - it doesn't feel off to me at all (I'm referring to Vaderios' mockup, not the original).