Arthur, I agree with everything you said. I just relayed how different post offices handle it differently, and that if placed in a postal collection box it is unlikely that they would dun you for the correct amount. .... ...... I always write "hand cancel" on my chip letters, and I always pay the 17-surcharge. (Here in Brooklyn it is impractical to wait on long lines just to hand the letters to a clerk. Recently I was in a suburban Illinois post office -- they had the same number of clerks (it seemed) and no lines.
In fact, most of the time I sandwich the chips between thick cardboard and pay the "parcel" rate. I was writing about common, strong, inexpensive chips in my post above, like the James Bond chips that I am selling 3 chips for $6 total. Never had a problem mailing them successfully.
Robert