Just think of the Figure 9 as being the 'loop' part of a Truckers Hitch. The Figure 9 can be positioned along the ridgeline so that the free end of the ridgeline can be passed around a tree and back to the Figure 9. Then pulled tight and tied off as described above.
Edited for spelling errors.
Exactly! Same thing I do on my tie outs. Add a length of shock cord above to the tarp grommet and adjustability is maximized. Where you position the fig 9 n the tie out will also dictate how much extra cordage you need as you are doubling back just like a truckers hitch.
"Qui non intelligit aut discat aut taceat"
(Who does not understand should either learn, or be silent.)