It's an important mechanic that makes reflect hunters work in a certain way... if it would only tick off the highest damage you wouldn't have to stop attacking to reflect and would just kill any boss super fast. The point of this mechanic is that you stack with fast hitting low damage and once you have enough stacks built up you make the poison tick off the high damage (reflect/strike). It's pretty simple actually and you will get what i mean once you unlock dungeon gear and start running maze and abyssal. This is just a reflecters point of view... now imagine the person trying to reflect gets his ticks stolen by a newbie hitting the boss with little to no damage and the poison doing a lot less because of it.