Harnesses are designed to stretch in order to decelerate your body in a wreck. Any bar within 6" of your head is fair game in terms of potential for hitting your head on it. When I would rarely drive my caged car on the street I would tighten my harness just as tight as I would on the track, I also had some dual density padding on the bars near my head that would provide an extra 3/4" of softer deceleration of my noggin in the event that my head did make contact. Just as a side note for anybody in this thread that already has a cage, pool noodles are not proper padding and will do zero to protect your body when it makes contact with the bars.