It will still deal the 120% even when redirected, since Punish doesnt replace the attack. Giant's Shortsword also repeats the same attack. The +20% is factored in first, so it calculates as if you had 20% more str not on the final damage. Something like pulverizer would then multiply that total so the order doesnt matter in that case. Something like Mercurial Mace which adds +15 dmg on the other hand, would not be affected by the 20%.