The screenshot proved your math was wrong. I do an average of 150 damage per hit blitzed + or - 30, and my sneak attack damage average is 123 + or - 20, So with all those boost running I should see (according to you) 723 damage a swing (150x2.65+123x2.65), which is double what I currently see. So no, your math is way off and it does not increase with helpless damage.
Edit= 2.65 comes from +50% base, +50% LD boost, +30% ninja spy, +30% sense weakness, +5% ship. I am also using shortswords so its not a handwrap issue.