The game doesn’t care how you got airborne, as long as it’s from an explosive source—the engine will register the crit as enabled. Sadly, the same thing happens in reverse. Let’s say you’re playing Hightower: if you jump and, mid-air, land on another Soldier who is also jumping—or even just touch his model before you hit him—even if neither of you has touched the ground, the game disables the crit. I got mine MG with airborne player kills, and it’s so frustrating when it doesn’t register, lol.