Experienced gained from an NPC = mobLevel * mobLevel * ZEM * classMultiplier (for level exp only) * groupSplit * groupBonus * serverBonus * HBM (leveling only) * MLM
ClassMultiplier is typically 1, 1.1, or 1.4 depending on class. This was put in place to effectively remove the class penalty during Velious, as the experience required per level is higher for hybrids and such.
groupSplit would be, for example, 0.2 in a five man group of equal level players.
groupBonus is either 0, 1.2, 1.4, 2.2, 2.6.
serverBonus is of course 1.2 for AK.
HBM is the hell level balance multiplier that applies to leveling from 30-60. For many levels this would be 0.9 and for hell levels this might be around 1.5.
MLM is a bonus applied if the NPC is within +/- 5 levels of the player. If the player is level 60 or higher, then for white cons it is (260-13*(playerLevel - mobLevel))/100. If the player is below 60, then it is capped to 2.6-((60 - playerLevel)*0.16). This value is then reduced or raised by 0.13-(60-playerLevel)*0.013 times the level difference.