Hero System Sixth Edition - Volume One:
When rolling the Killing Attack’s STUN Multiplier, add +1 to the number rolled for every level of Increased STUN Multiplier purchased. In other words, roll ½d6, then add the bonus from Increased STUN Multiplier.
The same amount is added to the stun multiplier from the hit locations table, when used. The hit locations table will be used in the event of "placed shots", but this means it will be used for the STUN multiplier (which will not need to be rolled) and the BODY multiplier, and the OCV penalty. "Placed shots" will be stock attacks (unaffected by martial maneuvers) but can have combat levels applied.
As an example, if The Stuntman had chosen a "placed shot" to the head of one of these brutes, his OCV would be reduced by eight. If his shot landed and did six BODY, the stun multiplier would come from the table (X5) before being increased by the levels of increased STUN multiplier on the attack (+2). The STUN would be calculated BEFORE the defenses are applied. In this case the brute would receive forty-two stun less defenses.
The resistant defenses would reduce the amount of BODY before the multiplier is applied, if the brutes had any. In this case, the six BODY would get through the defenses and be multiplied by the BODY multiplier for that hit location.