They are pretty small, low profile heads, but don't they have a little "kicker" tab on the back of the blades? Maybe your fletching is trying to turn the head the opposite way from the way the kicker tabs are trying to spin the head. If I recall correctly, NAP seems to be focused on right helical or offset as the way to fletch, since it is better to keep broadheads like the Thunderhead (with its O rings) tightened. Not sure, just a thought.