"Greatly reduces damage sustained in physical attacks."
Damage mitigation is done at a flat rate - whatever damage would have been done is reduced by a set amount - if the mitigation is greater than the total potential foe's damage then typically only 1 hp of damage will be done. The damage mitigation effects stacks additively with mitigations from other augments i.e. Autonomy, Bloodlust, and Fortitude. The reduction is taken after all other effects, such as striking resistances.