Thanks snowklinger and 509-pow for the efforts. I think I got it now. I think the first youtube link in 509-pow's post well explained it. I just realize that that's one setting I could (I never knew) change, and it appears it could be changed either way too, that is, either more parallel, or more unparallel.
May I assume that if I say "rotated the high backs", that would mean rotated the high backs to more parallel?
What would happen if the high backs are parallel, and how does that tie in with forward lean?