I'm confused about the way to set this up and have tired various formats. I want to have per item shipping (not based on weight at all) but I also need to have break points. So for example, one product, quite small and light has a shipping cost of 2.50. Another, quite heavy, 10.50. However I then want these to increment at particular rates up until say 48 items. After that I want free shipping. How do I set the table to reflect this?