Convertible top questions
 

I have a '99 Boxster Base with the original top. Lucky me it's in remarkably good condition. There has been a clicking noise directly behind my head while going down the road. Comes and goes with the quality (or lack there of) of the road surface. I did some investigating and found the cable from the rear top bow to the floor area was loose when the top was up. There is a bolt on the lower snap ball that adjusts the ball up and down. I can tighten the bolt and tension the cable to stop the noise. My question is, how tight should the cable be. To tight and it starts to pull the rear bow away from the compartment cover. So is just enough tension to stop the rattle enough? What does this cable do anyway?
Also, is there any way to increase the tension of the top header to windshield lock?
Thanks in advance for any guidance.
Jim