In the image shown below, the price in green should be either 2.90 or 8.60, but not 8.90.
Answer
Assume you have setup flat 3.00 shipping for domestic, and flat 9.00 shipping for international. Then create shipping discount profiles where you only add 0.10 for additional domestic items, and 0.40 for additional international items.
In Sandbox, you will see the international flat rate mixed with the domestic discount in the advertised savings display below.