I have 3 zones set up, one for the US, one for Canada and the other for the rest of the world. I ship with USPS - First Class, Parcel Post and Priority Mail. The flat rate module has been cloned to offer each zone the choice of using a Medium Flat Rate or Large Flat Rate box. The Medium Flat Rate box option is always the "chosen" option on the checkout page. The cart use to have the cheapest shipping option chosen before I added the flat rate options. Is there a way I can have the cart choose the cheapest option again?

Using 1.3.9g of zen cart.