So about factor_attackdir: MagicalSmalrusWalrusJones* gives this definition "Sets the percentage probability that an enemy attack will be ignored, and replaced with one of your attacks by individuals who are flanking." Essentialy, it's about the number of attacks counted, therefore a unit's attack, defense and armour stats do not come into play - it's like hit chance introduced in newer games. While my tests also confirm this explanation, I don't think Volcano (and some other mods) have the same opinion. In Volcano's, for example, what makes battles longer are changes to defense and armor divisors, which indirectly affect the relative value of those stats. I think he took factor_attackdir as a multiplier, and their values would nerf flanking too much. Still, this mod is a work in progress as it's a hell to test battles in TW - too much factors in play, very hard to set-up ideal test conditions etc. etc.

*https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=570444181