I beat it today on Hamada on the German Team. I was camping hard on A to get those headshots but i don‘t think you need to be directly in the objective zone, at least i didn‘t. But i could be wrong, because i had 27 kills at the end of the game and i am not so sure cause i wasn’t really aiming to beat this assignment. But i did all those headshots from the hills besides A and those are not in the spot. Maybe you just have to kill 20 people which are in Spot. But again i am not so sure about it xD