Do you have specific numbers or did you make that up? If you tank Melusine at the edge of the arena, she'll always turn her back to the tank for both Circles of Flames which allows you enough time to get Heavy Thrust or Impulse Drive in. Also, for monk, the effect comes from the form. The potency is affected by positionals. I would know if I hit from the flank or not by knowing exactly how much damage I should be doing on that attack (100 vs 150 potency, pretty easy to tell). Your flank is the same as my flank.