From Arelith Wiki
Effective Character Level (ECL) penalties adjust a character's level for the purpose of experience gain, to account for special abilities which give a character an advantage. On Arelith, these penalties come from gifts and subrace bonuses.
If a level 13 character has an ECL adjustment of +2, then his or her Effective Character Level is 15.
ECL XP adjustments are calculated as follows, and rounded down: (Level / ECL) x XP
A level 15 character receives 20xp for killing a NPC.
A level 15 character with +2 ECL receives (15 / 17) x 20XP = 17XP
ECL does not effect XP gains from roleplay bonus.