There was a very recent post by a current EQ dev from SOE about how AC currently works. It used to be very rare that they gave such specifics about a mechanic but they have been opening up lately, much to the appreciation of the players.
Here is the post:
Pretty deep explanation about AC
The post directly after his I thought was very funny.
I realize that this is an explanation for how it works in modern-day EQ(with Heroic stats and such), I just wanted to show people how complicated it is. I totally understand that it must be so hard to get that stuff right, so I certainly appreciate what the '99 devs are doing.
Also, lol at the "hi brad"