I just wanted to follow-up with my little adventure in Tare. I have it working just fine - thanks to all the people who have contributed to this thread and the other one. While it takes a little fiddling to get the calculations to turn out fairly correct, I learned a few things, at least for my business model, which involves very light items (~2 oz.) comprising relatively larger cubic space (55.35 cubic inches) requiring lots of protective packing and 200 lb rated cardboard boxes in a wide variety of sizes, depending on the order.

The first thing I learned is that the Tare calculation tends not to work as well for onesy-twosy orders as it does for orders of 3 items or more, but when it works (which is 90%+ of the time, it works well). The trick was to play with both Tare percent and tare weight. Second, the weight shown on the Shipping Estimator will only show Product weight, not total order weight (product plus tare), so you can't see the result of tare adjustments easily. Third, because of the second point, it is best to have a schedule of shipping rates from your carrier handy (I use USPS), so you can cross-check your results after you've made an adjustment. While the weights won't change in SE, the postage amount will correctly reflect charge for the total order weight. Fourth, since Insurance is a big part of how I do business, and thus needs to be included in SE, it absolutely necessary to set USPS calculations to "Retail" not "Online", as the online setting ignores your insurance setting.

Like I say, I just wanted to close the loop with everyone one this fun project. I am warm and fuzzy now!