Been putting up with the liner brushing the top of my passenger's head for quite a while... Figured it was just another "age-sag" problem. Checked it out yesterday with the roof in half-up position and discovered a plastic clip-strip (not to far from the zipper) that runs the width of the roof. It belongs on front edge of one of the frame sections. Bingo! My headroom's doubled.
Hope this helps someone at some point.
Pic showing strip with the end pulled off frame.
[/IMG]http://forums.rennlist.com/upload/cab_strip.jpg[/IMG]

 

Try again with pic.
http://forums.rennlist.com/upload/cab_strip_copy1.jpg