When I open mine that extra 1/2 inch I can almost hear something binding if I let it stop again on its own. So to avoid this, I simply try to stop it before it bottoms out. I like the look, because all the glass is hidden inside the roof.
BTW, haven't had a problem yet, but like I said I can hear somthing biding up if I let it bottom out. Other than that, its runs very smooth.
