USPS Global Express Rates are not accurate for me

If item weight total is 3 ounces, it will display a rate for 1/2 lb of documents when I'm selling non-documents. Non-documents have a minimum weight of 1 pound. This happens even if Global Express Nondocument is the only choice available. For example, to Australia, it displays a rate of $38 when it should say $55.

If the items weight is over 1/2 pound, it displays the correct price.

It gets inaccurate again if they ask for their product to ship in a cooler at a weight of 1.32 pounds, site returns price of 63.45 while USPS site returns price of 72.32 (USPS uses a shipping weight of 4 pounds) for Australia

Is this related? https://www.zen-cart.com/tutorials/index.php?article=85

What version of Zen Cart?
Which USPS patches have you installed?

Thanks for the suggestion, but that wasn't the problem. I decided to fiddle around to make most of the calculations correct though.
I had tare weight set at 0, I changed it to .25 pounds. Now when a 3 ounce item is ordered, its total weight is over .5 pound so the correct weight is calculated.
For the coolers, I assigned them a weight of 3 pounds, even though they are much lighter. This forces anything put into them up by the 4 pound rate.
There will probably times when customers are overcharged postage due to the tare solution, but at least I will stop hemorrhaging money on undercharged postage.

The mystery continues: There is supposed to be a 1/2 pound rate for non-documents....the site was actually quoting it correctly. Its a bug in the USPS Click and Ship site that won't allow the same rate. I'm putting my tare weight back to zero.

That just leaves the question of why cold shipping is inaccurate and I guess I have worked around that.