We currently offer flat rate shipping charge vary by weight which basically uses actual weight of each product. However, it doesn't work well for larger items low density items where dimensional weight becomes more important. There should be "vary by billing weight" method which looks at both cube and weight of a product. Dim weight divisor should be a variable allowing dimensional weight to be calculated using custom divisor (many shippers have contracts with custom dim weight divisor). Secondly, issue I see is in rate shopper from say fedex. It needs to use billing weight when pulling rates from the carrier. rates using actual weight doesn't work for large items.