Hello Sinbad, my recollection is that the rear rebound damping adjuster is from 0 to 2 full turns, per the owner's manual. And I think that the factory setting is one turn out (counterclockwise) from full rebound damping. I have the same bike as you and at 160 pounds with gear, I found it harsh too at first. But after having set the rear shock at minimum preload and the rebound at 3/4 turn out, I found it better but still a little harsh over jittery pavement. Then I fixed it by running the rear tire at about 37 to 37.5 pounds instead of the 42 psi on the sticker.
The tire pressure made a big difference for me. Maybe if I pillion a fat girl, I will have to increase tire pressure, but as it is it is perfect for me.