You aren't the first. I was putting 72c on bubble packs that weighed 2 oz because of the 12c for non-standard size, or thickness, or whatever of the regulations covers it.

37c envelope 1 oz
12c more for bubble pack Etc.
49c you are correct

23c for each ounce or portion over an ounce

Problem is the 12c only applies to the FIRST oz, so it's 60c for up to 2 oz, in a bubble pack.

1oz = 49, 2 = 60, 3 = 83, 4 = 1.06, Etc.

I receive chips, that people took to the post office with varying amounts of postage, not the same as the above, so there's a good chance the envelope you sent out, didn't arrive Postage Due.

I've sent out a single chip at 37c, before I understood the rules and to my knowledge never had one arrive postage due. It's one of those mysteries of life...