Its your overall defense, the resistances are just what you are resistant to. Higher defense means lesser attack and after that calculation, subtract you resistance. Say you get hit with 100 physical damage after defense calculation. You have 13% physical resistance so that 100 becomes 87. Dont know how the calculation between base attack and your defense would be. Maybe its subtracted so in this case you get hit with 500 damage but you have 279 defense so you only take 219 damage? Idk
Honestly, high defense is busted in endgame. I had a build that gave me +20 defense for every positive affliction I had and I had maybe 12 or so positive affliction during combat on top of my already high defense. I almost never went below 75%.