Shipping charges for Printify print-on-demand orders

I recently added a number of print-on-demand items to my Shopify store through Printify. By integrating Printify into my tech stack, Printify created shipping profiles with their shipping rates. Shopify is adding the weight of my default package (15oz) to the weight of the print-on-demand item (3.5oz) to determine the amount to charge for shipping. But this makes no sense to me since I’m not the one shipping out the item. My default package (a large box) has nothing to do with the print-on-demand items from Printify.

In researching this, it seems Shopify uses my default package to calculate shipping for ALL orders. Apparently, there is no way to tell Shopify that my lightweight little item goes in a virtually weightless poly mailer bag while my big, heavy items go out in my big heavy box.

Has anyone else encountered this and found a good solution? Thanks for your help!