It's not just axe heads. Dag frequently passes square sword tips as well, which most bel checkers would fail. The reasoning is pretty simple. The 2.5" rule is there to keep weapons from going into the eye socket and it seems to me the single most likely angle to hit someone in the eye socket is the 45 between the blade edge and the flat top. Therefore, it makes very good sense to apply the template to the corner of the tip of a sword or axe or whatever and make sure it won't go more then 1/2" into the 2.5" hole that represents your eye. It does vary, even among dag realms, but many of the biggest groups back east have a lot of square tipped swords on their fields (e.g. GvK has been pretty outspoken about not applying the template on a diagonal) so really it's up to you guys and how you feel about this safety issue.