The awesome effect of diminishing system starts at 7000def points = lovely 70% defense rate (means you take 30% of the initial dmg).
After that point you would need to get more and more def to keep rising def rate(meaning you want that def% not the amount of def you have).
Knights could get close to 7000 def, thats like 67% def rate(if i recall, tiduspeco did a topic where are the value)
Warriors could get 8000def thats like 72%
And bms got over whooping 10000def which is 75% def rate. Meaning if you can get +7000 def from just making 2-3 armor piece to +20 from refining you would have normal tanks def :/
I would say defense %cap is like 80-90% but you would need over 20-30k def (which is srsly totally pointless when you dont gain athing from it).
If someone has more than 10-15k def would like to ask player to screenshot and show def% just to confirm this.
Refining armor is good for other than tank class, but from getting same def than a tank is just wierd seriously :/
Btw i played as a warrior with 3 pcs of +20 on armors and my headgear has +7.. just to be exact
as of now i already have 20890 Defense (i'll put screenies on it).. but having huge additional on my defense doesn't inflict any reduce on damage taken from monsters..
I have tested on FF and chaos dungeon..