Zombie spawn location ect

[trickkynickk 2]

Ok so its my 2nd day playing and i dont know half the stuff to play right but i have noticed the zombies spawn very unusually. They just appear behind me sometimes and i had walked through where they should have been its very suckish. If there already isnt there should be a distance that zombies can spawn behind you if your walking somewhere ive lost very hard earned guns that way so if this post is useless just close it but reply if not