I am not an aviator either, though having a long sim experience with Red Baron I & II and 3d with Western Front patches

This means I absolutely don't have a clue on how to to fly a WWI plane and how to effectively shot.
Well, you can find some help from real pilots autobiographies and letters, and I rememebr I never have heard anyone bringing down planes from a long distances, apart lucky shots, like the one which bring down Richtofen in 1917.
You easily find reports of MVR around, where he talk of distances like 30-40m, I got some from
Francesco Baracca which talks of such close distances too, maybe closer too when he used to fly a Nieuport 11 and shot "under the belly" of Austro-Hungarian recon planes.
To fire from more than 100 m to an enemy target would be a waste of ammo, in my opionion

Anyway, while I used to PLAY :P I had the better way from 0-60 m. But that was a game.