VERIFIED SOLUTION i

How to get separate rates for 1oz and 2 oz First-Class Letter Single Piece rate mail in MailStream Plus

MailStream Plus™, all versions, all platforms
This is controlled by the ALG PS parameter.  By default, position 20 is blank, so pieces of both weights go into the same tray and get the same 'blended' rate.

If ALG PS position 20 has an S, then the different weight pieces go into separate trays (by ounce weight), and then will pay the rate based on their own weight.
UPDATED:  May 14, 2019