Perhaps you can clear up my confusion. I have worked on this for over two hours and I still cannot get it right.
I am shipping using UPS rate lookups.
If I sell a very heavy item to Oregon, 97032 zip code, the FedEx cost is $133.66 because it is oversized and weighs 1248 oz. I have configured the box to accept only one item. I have fiddled with the weight and cost of the package and the weight of the item to make it come out to the $133.66. That is correct.
If I sell one 2 oz item in a small box, with a 20 unit box maximum, I have it charge 8.99. That is fine.
Now, here is the problem. If I sell one heavy item at the same time as I sell one 2 oz item, it over charges the shipping. It isn't $133.66 + 8.99 or $142.65, it is $150.39.
This represents an overcharge of $7.74. I thought that it looked at each box as a separate unit, unless I chose to combine them.