Definitely head up. But not a fan of the aim low method. If they deer doesn't duck, (and inside 20 yards, they rarely do) a lot can go wrong. Very small target at the bottom of the chest cavity. 1" forward and that knuckle can stop the arrow. 1" low or shooting with any down angle and you might barely clip lung, single lung, or miss low. A few inches rearward and you get into stomach. The stomach comes way forward in the bottom of the chest cavity. Head up, aim halfway up the lungs, pretend the heart doesn't exist, broadside, keep shots a reasonable distance, and things rarely go bad.