If you use a hollow-core braided line like Amsteel (or even something smaller like Zing-It) you can make it adjustable by making what amounts to an extra-long whoopie sling - no hardware / no added weight. One end has a locked brummel and the other end is adjustable (put that end down by your feet so the tail doesn't hang in your face. If you find yourself not adjusting it anymore because you like where it is, just pull the tail out a little, cut it off and bury it back in the hollow core - viola! a fixed ridge line.
Having said all that, you don't "need" one. After you hang a few times, you can get the angle right without a ridge line. I mostly like mine for hanging things off of it and keeping the bugnet off my face.