Work case:
Level 31 Mystic, Realm 3, name
Woswaldo.
Excerpts from the combat log, relevant part in red:
Team 2 takes turn
Damage reduced from 128.457 with 8
Heretic - Archer hits Woswaldo for 120.457 and the latter is left with 767.16 health.
Damage reduced from 28.0109 with 8
Plain lion hits Woswaldo for 20.0109 and the latter is left with 747.15 health.
Plain lion 4.53/22.777777777778 Block successful.
Woswaldo tries to counterattack Plain lion.
Woswaldo hits Plain lion for 63.7877484 and the latter is left with 768.21 health.
Monster kills bonus adds 8% to damage.
Plain lion 98.77/35 hit evaded.
Heretic - Archer 2.18/22.777777777778 Block successful.
Woswaldo tries to counterattack Heretic - Archer.
Woswaldo hits Heretic - Archer for 80.539827133333 and the latter is left with 335.46 health.
Monster kills bonus adds 6% to damage.
The fight is still available in his profile, it's the last one (first from the top), the combat quote is from 7th turn.
The mob in question has 367 armor.
Now for the calculations
80.53 (the damage inflicted)/1.06 (given the 6% bonus from monster kill bonus)+367/15 (armor mitigation, 24.46 damage mitigation)=100.4317 total damage inflicted before mitigation.
Now, the character in question has 3/6 in counterattack hence he counterattacks with 45% of the damage. 100.4317/0.45=
223.1816 which is in line with the paper doll shown damage,
221 given the round ups and whatnot.
The problem is the character in question has a staff equipped that provides
Counterattack +3. So he should have Counterattack 6, therefore should hit for 80% of the damage mitigated by armor etc.
I verified with another character that has plain 6/6 counterattack (
MDMD, realm 3) and she hits for 80% from the maximum damage shown on paper doll, mitigated by armor, obviously.
The only viable conclusion is that the bonus doesn't work.
P.S.
The character in question (Woswaldo) has downgraded (hence re-skilled) Counterattack 3 given the fact that you can't have more than max rank using bonus skill items