Much farther I beleive if I understand your question. I am currently using no Labels but am considering trying Robert_Wiggins "Friendly only" Label mod since most everyone is in the same skin.
On that subject so I don't light up every Friendly in a 15 mile diameter I have to look at the Workshop Settings to limit Label range to something where I would realistically see a friends face, cap, jacket, or distinctive quirk on his plane.
And now that I typed that is that what you were referring to above? If so, to average out the above things you would be looking for I would guess 100-150 meters?