Hi Roger. Basically, in addition to the forward-back and tilt-up and down, there is a little thumb-screw on each - I don't know what to call them - cheek holder, I guess. This allows you to move them closer together or farther apart along the sideways horizontal bar they attach to. It took an adjustment after each of 3 or 4 rides to get it so they were placed correctly under my "sits" bones.
It is a very individual thing to get right. When I got my free 6-month tuneup, the guy at the shop said he couldn't understand how I could ride it. He couldn't get comfortable on the seat - it kept pressing on the back of his thighs.
But once it fits, numbness is a thing of the past.