A high defense skill % mod is pretty awesome for a tank, and contributes AC that affects avoidance but not mitigation. My understanding is this:
All classes have an AC softcap, and there is no hard cap for EQemu servers unless it was explicitly put in (take that with a grain of salt, because I haven't verified it).
According to our ChaosSlayer (/wave!):
http://www.eqemulator.org/forums/showpo ... ostcount=1RULE_REAL ( Combat, NPCACFactor, 2.25)
RULE_INT ( Combat, ClothACSoftcap, 75)
RULE_INT ( Combat, LeatherACSoftcap, 100)
RULE_INT ( Combat, MonkACSoftcap, 120)
RULE_INT ( Combat, ChainACSoftcap, 200)
RULE_INT ( Combat, PlateACSoftcap, 300)
RULE_REAL ( Combat, AAMitigationACFactor, 3.0)
RULE_REAL ( Combat, WarriorACSoftcapReturn, 0.45)
RULE_REAL ( Combat, KnightACSoftcapReturn, 0.33)
RULE_REAL ( Combat, LowPlateChainACSoftcapReturn, 0.23)
RULE_REAL ( Combat, LowChainLeatherACSoftcapReturn, 0.17)
RULE_REAL ( Combat, CasterACSoftcapReturn, 0.06)
RULE_REAL ( Combat, MiscACSoftcapReturn, 0.3)
RULE_REAL ( Combat, ACthac0Factor, 0.55)
RULE_REAL ( Combat, ACthac20Factor, 0.55)
If you look closely, you'll see all of the softcaps. As a warrior, you're looking at
300 + (35 + 2 from max def AAs) for a total of 337 raw ac softcap.
Once the cap is reached, all raw item AC has a diminishing return of 45% for warriors.
Let's say your warrior has 7630 raw AC from all items and augs (no buffs). You then have
337 + (7630-337)*.45 = 337 + 3281.85 =
3618.85 total raw ACThat's right your AC is not nearly effective as #mystats might have you believe.
Raw item AC determines your mitigation and chance for enemies to 'miss' attacks on you. Generally, the more AC you have, the more likely the hits against you will not be max hits. I have witnessed tanks with 1k difference in AC take the same max hits on THF, fwiw.
Avoidance AC from from agility and defense skill contributes a different kind of AC. It has no effect on mitigation, but it does affect your chance to avoid damage. I don't know the raw numbers, but my anecdotal experience was that defense skill mods are pretty awesome.
Shields are exempt from the diminishing returns. You will get all 100% of the shield AC and any augs on it, but it's unclear to me whether the shield must be in the secondary slot or not to qualify.
If you'll take a look at
Urahara (I'll pick on Beatboxin for a moment!)
You'll notice that he used to wear Shield of the Omniscient in secondary, but swapped it out for one with 4 aug slots. Why? Because he can and should pile up ALL of the AC that he can on a shield because it's penalty-free. He is getting 615 raw item AC from his current shield. Smart guy.
Further reading:
http://samanna.net/gen.info/effects.shtml#4http://forums.station.sony.com/eq/index ... d-you.160/http://www.monkly-business.net/forums/s ... hp?t=16555