I did a quick calculation to get an idea of the link: Level <-> meters / pixel
! Warning value can vary according to the distance from the equator but it already gives an idea ....
at around 15 ° latitude a Level 11 cell is about 18.4 km wide (see on a grid generated by AFS2 Grid generator) knowing that in the .png files generated to make .ttc and .tth files are a size of 2048x2048 pixels, I deduce (rounded values):
Level 7 -> 147.26 m / pixel
Level 8 -> 73.63 m / pixel
Level 9 -> 36.8 m / pixel
Level 10 -> 18.4 m / pixel
Level 11 -> 9.2m / pixel
Level 12 -> 4.6 m / pixel
Level 13 -> 2.3 m / pixel
Level 14 -> 1.15 m / pixel
Level 15 -> 0.6 m / pixel
correct me if im wrong...
I attempted calculating this once as well and from what I recall my results were pretty similar (except I did it at 45 deg latitude). The one thing I wasn't sure of was if the effective resolution really does change with latitude, or if there was something in how Aerofly handles it that somehow makes it more uniform for all latitudes. I suppose this makes sense though, because orthoimagery is going to be artificially stretched at higher latitudes anyway, which reduces its effective resolution, so maybe the two effects cancel each other out.
Now you've piqued my curiosity again... I might have to calculate this as a function of latitude and see how much it really varies. It is definitely useful knowledge to have, because there's no use in spending a ton of time downloading orthoimages at 1m/pixel resolution if you're only planning to convert them at level 13, for example.