on mine the 5th line goes from the chicken loop ,thru the bar then follows the front lines going thru stays/loops to keep it running with the front line. when the front lines split to go to there different side it continues straight to the connection point .
as far as tuning it ,i belive its kept slightly slack .

You know how you had to swim towards the kite to get it to roll on it's back... guess what? NO SWIMMING! :D
Just pull that fifth line in as much as you need to get it roll on it's back.

and one of the best things.... now self landing is really easy and safe. Just unhook and throw the bar....

5th line kites rock.

Hard to be certain without seeing your kite but i would aim to switch the safety over to the 5th.

See if you can find another small stopper ball (SS etc make em) and put that 1/2 the size of the kite in metres up the 5th line. For a 15m kite - put it 7-8 metres up the line from the bar. In the event of bailing to the 5th your bar will only slide up to the stopper ball (not all the way to the kite) which should be more than enough to fully depower the sucker. This also means in bail-outs you may well avoid tangles and be able to re-launch from the water.

As with anything - test this in a reasonably controlled situation - not when the brown stuff hits the fan.