Doing some digging to find out how this whole thing works.
Once the billing info is entered the page is submitted to:
OrderCalculate?updatePrices=1&calculationUsageId=-2&orderItemId*=&quantity*=&URL=OrderDisplay?langId=&storeId=10054&catalogId=10002&orderId=7609120&shopStoreID=10052
calculatioUsageId=-2 tells it to apply the shipping discount. From what I can tell the discount is entered in accelerator and uses the promotion configuration files. Trying to get a copy of that file to see what the settings are. Found this in the documentation:
<MonetaryValuePresence>
<Price>true</Price>
<ShippingCharge>false</ShippingCharge>
<Tax>false</Tax>
<ShippingTax>false</ShippingTax>
</MonetaryValuePresence>
Does this determine which values to use in determining a promotion? IE if tax was TRUE than include tax in determining if you qualify for a promotion?