On long range missions, for example Gotha raids, you also need to cope with the fact you may be flying to another country to fight - so culling flights based on a small circle will kill that campaign mission type.
ME's Plane culling feature does not cull planes around player in small circle. In fact, it creates polygon copying player's flight path in choosen distance (how it say in English - equidistant?).
...it doesn't break escorts or other missions
Mission Editor 1.8.2 should already solve that problem and does not break any mission. Available below for download.
Flight paths after culling (in red and yellow):
Culled flight paths (in black):
Player's flight paths in green