After a sleepless night I found my answer: I removed the port side (left) locking bracket from the seat. Some officious designer decided "if one latch is good, two must be better" thereby creating adjustment problems by having two latches controlled by one switch. Years of trying to keep Model A Ford mechanical brakes adjusted taught me to see the mistake in this design. The left side latch is superfluous any way: remove it functionally, fine tune the right side cable and be done with it.
Now I'd like to have five minutes alone with the designer of that seat. I guess no one in Taiwan spends more than ten minutes riding their scooter, so a stuck-in-one-position saddle for someone less than 5'-8" tall is fine design in their eyes.
If it wasn't for this wonderful forum I'd be long gone from Kymcos, I'd be riding and wrenching on Hondas or Yamahas. Thanks for sharing, guys....