I typed words in google and pressed butan... found this little gem:
http://teir-dal.tripod.com/id47.html
2.18. How is backstab damage calculated?
Nothing is official, but the general belief is that at low levels, it works something like this: Assuming that you are using a weapon deemed 'acceptable' for your level (i.e. not too powerful [some players report getting very high level weapons at lower levels and not getting the damage they were supposed to until they leveled some more]), max damage is calculated as: (DMG * 2) + 1 Backstab simply multiplies this by a constant factor. We approximate this factor to be:
(BACKSTAB_SKILL / 25)
So a maxed level 10 rogue has a backstab multiplier of (55 / 25) = 2.2x. Assuming he's using a giant snake fang (DMG 5, so max damage (5 * 2) + 1 = 11), his level 10 max backstab will be (11 * 2.2x) = 24. Backstab damage caps at 25 * DMG at level 50. Towards level 20, these numbers skew. Backstab seems to top out for a time, and then go up rapidly in the higher 20s. Strength effects how often you hit for max damage, so be sure to have STR enhancing equip and/or STR buffs on you as often as possible.
At 51st, the new minimum backstab damage is Level*3/2, rounded down. 76 is the least you will hit for at 51st, and it goes up. At 60th, the minimum backstab is Level*2 (120).
This doesn't specifically say anything about AC mitigation but I'm looking for stuff.
From this source (talking about very recent expansions)
http://www.thesafehouse.org/forums/s...ad.php?t=36486
That's the maximum hit of course. Minimum hit (assuming sufficiently high damage on weapon) follows a different formula, and the whole slew of hits come from a mixture of damage intervals (the 1 to 20 roll that all NPCs get) and a PC specific roll between 1.00 and 3.55 in 0.01 intervals. The rolls get multiplied together and due to a non-uniform distribution (eg rolls of 20 maybe very common when you have
high atk vs low AC on a mob) in both DI and PCroll values they show up as a series of larger and smaller spikes on the damage frequency charts.
There is still indication that the melee code follows the same rolls as we see everywhere even on P99. Maybe the AC values are the cause?