I will not mail using the postal service for that reason. Using the same person at my small town post office and she's interpreted the rules differently for much the same envelope.
So, I bought me a scale, read the guidelines the USPS puts out, spoken with my wise Canadian friend Bru (sandyrusty/sandy's singles) and have been trading regularly with him using those ideas bandied about.
If our Canadian friends are saying it's okay to mail using PWE, large business envelope, and all the other hints, and you still wish to use bubble mailers, boxes, etc. then you'll pay those exhorbitant international prices. That IS the uniformity.
Because of the way it's been explained many times on different threads including this one, I'll continue trading with Canadian partners with a max of 180-185 and willingly spend $5.83 for postage. Or I can choose to send as a bubble mailer or box and pay $17.25. It's a no-brainer.
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“Aslan didn't tell Pole what would happen. He only told her what to do. That fellow will be the death of us once he's up, I shouldn't wonder. But that doesn't let us off following the signs.” - Puddleglum in The Silver Chair by C. S. Lewis