So, at the moment Heavy Handed effect to some unarmed weapons and they have different strength penalty to get knock down.
Unarmed / 5ST penalty.
Brass Knuckles / 4ST penalty.
Spiked Knuckles / 3ST penalty.
Power Fist / 1ST penalty.
Mega Power Fist / No ST penalty.
This is my suggestion.
Unarmed / 6ST penalty.
Boxing Gloves / 5ST penalty.
Brass Knuckles / 4ST penalty.
Spiked Knuckles / 3ST penalty.
Power Fist / 2ST penalty.
Mega Power Fist / 1ST penalty.
Personally I think that Mega Power Fist should not have 0ST penalty, atleast 1 to prevent some things.