I have my default package set, but if a customer orders 9 items, Shopify is assuming that all will fit in that one package. Is it possible to set it to one item per package. Otherwise the quoted rates from UPS are only accounting for the single package and the weight from all included items which greatly under quotes rates.
Can I know what is the default shipping option you set up now as? If you set up the default package based on one product, are you getting relevant rates when your customer orders 9 products? I’m not sure if this would work since Shopify doesn’t offer multiple package sizes, and you can only set up a default box for all your products. For a better workaround, I suggest you check out our Multi-Carrier Shipping Label App. You can easily choose the packing method based on your choice with the app. For your requirement, you can choose the quantity-based packing method in which each of your products will be packed in separate boxes and the rates will be calculated accordingly.