I always put the small piece of paper in my crucible but notice that it doesn't make a difference if packed good and tight with coal. I take my lid off right at the tank but believe that since the coal pack is at such a temp any oxygen will be burnt immediately. When I crack my oven at quench time there is always a subtle flame from the lid as oxygen is entering the oven chamber and being burnt. That is why I have made a longer crucible so that the parts sit deeper in it preventing any oxygen exposure causing a flash burn. At 1375F any oxygen is going to be burnt nearly immediately.