I don't understand why planes would come from any direction but your own base. Planes coming in from enemy territory doesn't make much sense.
A good amount of Lend-and-Lease stuff was shipped over the Atlantic ocean in the north and was target of german intercepters. That's basically what those supply planes coming through enemy territory represent. However, the main reason is obviously the possibility of counterplay for the opponent.
Relic Entertainment
보드카 중대 
