Hello @GrinoC thanks for your post. Check your shipping and profile and see if the profiles are set for "rate charge" and if it's "per order" or "per item". This could make a difference. You could also try a shipping profile based on the total for the whole order, and create a $12 charge for a dollar amount over a certain amount. (I'm guess the small and large items are priced accordingly so if a buyer puts small into their cart and then a large, the total dollar amount sold would reach a level to push the shipping up )
