Shipping costs are a tough nut to crack, even in the lower 48. UPS kinda reminds me of airlines in that prices seem to change from day to day for identical packages/destinations.
UPS in particular seems to want nothing to do with Alaska & Hawaii (Canada too); their rates are generally 2X+ those of USPS and delivery times are much longer (outside of the Expedited Next Day & 2-Day services which are eye watering as far as cost).
While e-commerce systems (where you can define size/weight of individual items) are generally tied into shippers directly in hopes of determining accurate shipping costs, it becomes a bit more interesting when 15 items that can be on an order to be shipped in a single box present themselves.
I have no idea how the e-commerce platform tells the shipping software how to determine a shipping cost for presenting on the checkout screen for multi-item orders…really fuzzy math perhaps? I do know that when we were using ‘calculated costs’ for shipping, it got somewhat inconsistent…and on the surface, arbitrary as to over/under vs real costs.
In the end, barring anything like artificially inflated shipping/handling add-ons, shipping generally ends up written in red ink on the ledger as opposed to black. The inconsistency led to our current $9.99 flat rate for orders under $99, Free Shipping for over $99 policy (within the lower 48 states…doh!) Then when you ship a $600, 65# pressure washer across the country on a Free Shipping order, welcome to ‘The cost of doing business’ as you slap that $60 UPS label on the box.

And there isn’t much margin on some things unless you buy a few containers full…a bit impractical for some.
It’s all in the math I guess, something I never excelled at!