you said before that you wanted to discount the entire shipping if quantity was greater than 1.
to discount $3 for each item over a qty of 1, use the same trigger:
"subtotal for any column" - if the subtotal of column 'quantity' is '>' a value of '1'
for the calculation use:
"Based on multiple of column subtotal"
subtotal of column 'quantity' times '3' 'minus' '3'