Thats a good point, at altitude I dont think they could smell the flak as they would be wearing oxygen masks. I know the germans used throat mic's so I guess they would have had a choice if they were at a lower altitude as to wether they wore them. But the RAF had the mic set in the oxygen mask so they would have to wear them if they wished to be able to communicate without using a hand to raise the mask to their mouth i presume.