I'm still curious how attack rating is calculated
I did make some additional testing during pub duels when I ran into people
damage to attacker from thorns auras definitely kills them in one hit if they connect. Damage from shiver armor can kill them, but I still landed some hits so it can't be doing it exclusively before they attack and always killing in one hit, or else they'd never land an attack. I've been able to attack people with stormshield without ravens dying, so I can't imagine lightning damage to attackers does much if anything. I'm unsure how raven HP is calculated, the game lists 20-32 base HP in monstats.txt under the same parameter list used for norm. If its adding the monLvL hp modifier than its a whole lot higher, since they use lvl = slvl+clvl-2, which for a level 99 druid with 53 raven, assuming it caps at 99 (table only goes up to 110 anyway) it would be +3940 AR, +7792 hp. I don't think that's consistent with them dying to shiver armor on sorcs, but if they only had 20-32 hp then stormshield DTM and other low sources of reflect would kill them. Thorns would kill them in 1 hit even at 7800 hp, and it sure does.
but the AR question is whether that +3940 is applied before or after their % AR bonus. They have 85 + 15*slvl + MonLvl AR listed but also got +1660% ar at level 53, so if its applied before %AR, that's 85k ar, if its after, its 19.4k ar