From BuffHeavyFighters.entity:
entityModifier
buffEntityModifierType "PhysicalDamageAsDamageDealer"
value
Level:0 0.120000
Level:1 0.220000
Level:2 0.320000
Level:3 0.410000
entityModifier
buffEntityModifierType "ArmorAsDamageTarget"
value
Level:0 2.000000
Level:1 3.250000
Level:2 4.500000
Level:3 5.750000
Yeah, I think it just increases the weapon damage by 12%, 22%, 32%, 41%. Not totally sure though.