I looked through a few pages on the forum here and it seems there are a few related questions but no answers to them. Hopefully my question will spark an idea. I did figure something out from the forum posts. The maximum shipping weight is one thing that was tripping up my shipping calculations.
Here is what I've got. I've got (among other things) two items I sell. You can buy these items in "kit" form for a little cheaper. Basically it's just like if you added the two items to the cart and checked out except you're adding only one item to the cart. The shipping module (UPS and USPS) doesn't realize I am shipping these as two separate items (just like if you bought them separately, I have no way to combine them into a larger box). As such it grossly under calculates shipping charges.
What helped was dropping the maximum package setting from 150 to 50. The "kit" item weighs 65 pounds so it correctly split it into two boxes but it split it evenly (as possible anyway). This helped but it is still calculating about $10 too low compared to my negotiated UPS rates which means I loose money on shipping. I'd prefer if it showed me retail published rates so that for cases like this I have a buffer.
While we're on the subject, how can the UPS/USPS module take into account box dimensions and other options such as delivery confirmation and insurance? I'm sure that is part of what is eating up my difference in calculated shipping costs and actual costs. Right now I have a $10 handling fee for UPS and $5 fee for USPS just to make up some of the difference. Imagine if I didn't have that in there, the example above would be $20 short on shipping costs.
I think I can take care of the two items into one issue by using attributes on one or both and not have the separate item to combine them. In other words since both items are available separately I remove the combined item and offer the other item as a bundle option. The cart should show two items, both should be below the max shipping value and should properly calculate as their respective boxes (I hope). The other option I had was zone based flat rate shipping on these particular items only. It's not what I'd want to do but it's an option.
Joel



