I'm guessing that it might have been possible for a WW2 pilot to see planes 7 to 8 km away under perfect conditions, but people tend to forget that WW1 planes were tiny compared to WW2 aircraft. These are small single seat aircraft, barely more substantial than a modern ultra-light. And they are not shiny metal or painted bright colours like a modern Cessna, they are camouflaged. If you read some biographies, it becomes apparent that pilots had a hard time seeing aircraft, often even at very close range.

I find that I can spot planes at about 3km using no labels, if I am very sharp. I think that might be a bit shy of real conditions, but I don't find it unreasonable when compared to historical accounts I've read. But what do I know? Anyway, I like a challenge and I like my screen clear of any techno-junk, so I'll be firmly in Level A and probably dying regularly.

The more unrealistic problem, and this only my amateur opinion, is that the AI pilots see significantly farther than the player can. If I could find the setting for the AI's sight range, I'd love to fiddle with it and try bringing their sight distance down a bit.