The way I see it the fighters ability to hit someone when they shift away is not something the npc knows (the mark is what is affecting them so they know about that and lots of characters mark and npcs that mark are not generally a duplicate of any given defender power, and I consider it consistent an enemy doesn't magically know when they ignore the Swordmages mark he will be teleporting to smack them either). So you can expect if they would be frustrated by missing or simply want to kill those obviously deadly others or the guy who keeps healing others or whatever reason like they have a good charge they want to use, shifting then doing the charge is the order of the day. The defender of whatever stripe I would say gets at least one provoke possibly per enemy.