Just as Swamp Collie said it is bullet placement. High hits on deer tend not to bleed out as soon as low hitson deer.
This was stated in an archery forum. The theory is that the animal will bleed internally until it fills with enough
blood to bleed out the holes created by the bullet. Like pail with a hole in it. I don't know if this is true but it does
have some merit behind it in my experiences. That is that deer hit high do not leave blood trails for a while. But it is also
my experience that deer hit high tend to not run as far either.