I shoot at the middle of what I can see, if someone's only sticking their head out then my point of aim is going to be their nose.  Likewise if someone's moving quickly and I full auto at them to increase my chances of a hit and some of those shots hit them in the face/head, tough luck.   If you don't like getting shot in the face, wear a full face mask.   Only time I have ever complained about being shot in the face is when I got a row of 5 full auto shots across my face with my arms up and a red rag on my head from about 15' away while stood in the open.  The guy claimed to not be able to tell I was dead... I had a bit of a flash at that.