I just happened to think about you saying that your head would be one inch away from the roll bar and I thought I'd make that one inch of foam padding. Well, that wouldn't look very good and I don't really know how effective it would be. Then it came to me. Why not suspend a headrest from your roll bar like some race cars have. Then you wouldn't have to worry about your head making contact with the bar behind you.

Sorry, that's the last thing I'll say about the roll bar. Sometimes I get hung up on these things.