How is the + defense for shout calculated?

[wheel-of-doom]

I tried searching the forums and arreat summit says nothing on the subject.
Since +520% defense doesnt give me 30kdefense when my base is 6k, how does it calculate the amount of defense you get?

[Wacken]

I tried searching the forums and arreat summit says nothing on the subject.
Since +520% defense doesnt give me 30kdefense when my base is 6k, how does it calculate the amount of defense you get?

I don't think your base defence is 6k.

Base defence is all your items defence added together. (don't think 6k is even possible there)

Then, add together the bonusses (shout, ironskin, maybe merc) and apply the total bonus.

So it may be like this:
Base defence 3k.
Iron Skin 100%. Without shout, you show 6k.

Now you shout, add 520% for total defence bonus 620%.
3k+620% = 18600