Quantity item shipping USPS for USA only

[mrcastle]

Hi all. I'm trying to figure out how to setup shipping for first class usps quantities.

1) I currently have a flat rate shipping rate of $3.49 to anywhere in the USA (I only ship in the USA)
2) If your order goes over $20, shipping is free.
3) My problem now is if you order 2 pieces, shipping goes up to $6.98 and for 3 pieces it's $10.47 ($3.49 x 3) so I know I'm losing additional business big-time.

So, I need to input these figures (not exact) but you'll get the idea:
Qty 1 $3.49, Qty 2 $3.49, Qty 3 $3.99, Qty 4 $3.99, Qty 5 $4.49, Qty 6 $4.49

My sheet music is typically $2-$3 so after 5 or 6 pieces, the $20 free shipping rate should kick in. I'm attaching pic's of the 2 modules I use. One for free shipping and the other for the flat rate.

Hope I've made this clear enuf... thanks for any help you can give