You can configure shipping costs for items within a specific assortment and for items within a specific subcategory within that assortment. This ensures that shipping costs are only applied when items associated with that specific assortment are ordered.
To configure shipping costs, navigate to Administration > Shipping Costs in the CMS. Here, you can set shipping costs for specific assortments and subcategories. Read also Why are there no shipping costs calculated for the order?
Then in the drop-down list behind 'Item class', choose which assortment these shipping costs apply to. If the shipping costs only apply to a specific subcategory within that assortment, use the 'Item class value' option to select the subcategory.