in siege mode i can understand you missing a guys head even tho its dead on. I fired 5 or so crossbow bolts at a guys head and wondered why he didnt die up on the wall. While storming i got closer to the where i was shooting and i noticed the colision mesh around the wall is actually higher than what it is visually in areas. The arrows ended up stuck in midair. Sometimes i find shooting from another angle made the difference but i have noticed that problem.