When I sit in a forward-facing bus seat, my knees aren't wedged against the back of the seat in front of me. I took a picture:
I've lost my butt shelf. I can now feel the entire length of my spine resting comfortably on the back of a chair, or against the back of the bathtub. It's a strange feeling, not having that gap between my butt and the center of my back when I sit down. I don't think the small of my back has had contact with anything other than my bed in a LONG time. My back feels better too!
So there's that,