You probably can't win an argument with a postal clerk. At least I haven't been able to. Response is "How long have you been handling the mail? I've been doing this for 30 years!"

The postal manual is not clear, and it can be interpreted to mean you are shipping a 1st class package.

I can only suggest you use a different branch. Or ship I in a bubble envelope and use PayPal to print a label. Should be under $2 for up to three chips sent as a 1st class package. And the chips do get more protection that way.