Tommy,
I think you are correct that the instructions for tying the taut hitch as shown are not as clear as they could be. Following the instructions and pictures given with the white line there is just no way that I could end up with a knot that looks like the final knot shown with the yellow line.
That being said - I think the key in their instructions is that the the tarp line is to be held tight after the clockwise pass around the tree and is not tightened any more by tying the taught hitch knot and sliding it toward the tree. In other words , the knot shown is only to stop the slankening of the tarp line ( or ridge line ) tension already pulled on the line.
The last sentence in the intoductory paragraph states that the ridge line ( or tarp line ) is to remain taught from that point onwards. So it , the ridge line , is not tightened any more by sliding the yet to be tied knot toward the tree. Thus this knot appears to only be useful in preventing the loss of line tension already pulled on the ridge line.
The bights put into the knot appear to me to be only useful to make this a slip knot to be easily untied by pulling on the free end when you want to untie it. Also note that the instructions state that the knot needs to be tighter to the tree than shown in the pictures, which I think is the second key to indicating that this knot is only intended to hold the tension already pulled on the ridge line and not to adjust it tighter by sliding the tied knot.
I think if you think about this knot with out the bights or loops tied around the tarp line with the free end you will see that basically you take the ridge line anti clockwise around the tree, put a bight around the tarp line , and go back around the tree in the clockwise direction and pull the desired amount of tension on the ridge line and hold it taught from that point onward. Then - if you leave out the double bight or loops tied with the free end all they are really doing is tying a half hitch with the free end around the taught tarp line and pushing it up tight against the bight of line which first crossed over the ridge line and then making an overly complicated slip knot to hold tension . Thus I think it is only a tension holding knot with somewhat complicated quick release slip knot to hold it all together.
I think if you want to use their technique the whole thing would be simplier by just making the double pass around the tree, put a half hitch around the ridge line with the free end and snug it up and then tie a second half hitch around the tarp line with a loop to make it a slip knot to be easily untied when finished. But in the end I think there are easier or better ways to tie a taught ridgeline.
Anyway , that's all I could get out of the instructions playing around with a bit of line around a a chair back post and trying to follow the instructions. Perhaps I am still getting it wrong as I could not get a knot to look like the knot in the yellow line which appears to have a half hitch tied with the free end just after the reversed pass around the tree which is crossing over the hanging down loop.
For my own use , I find the best way is to just take the ridge line once around the tree. Go back a few feet from the tree and put a trucker's loop in the ridge line. ( sort of a over hand knot tied on the bight leaving a loop pointed toward the tree, the artillery knot and figure 8 loop work well too ) pass the free end through this loop and pull the ridge line tight by pulling the free end back toward the tree. Then just tie a looped half hitch with the free end, tied with a loop to make it a quick release slip knot. This tie off slip knot can be tied either around only the line coming back from the tree toward the tarp or tied around both lines, ie the line going to the tree ( the tarp line ) and around the returning line together. This method is taught by Cliff Jacobson in his Forgotten Skills dvd. Is simple to tie and adjust again later if needed.
You might find these pages useful
http://www.netknots.com/html/outdoor_knots.html
http://www.realknots.com/knots/sloops.htm
http://www.iland.net/~jbritton/inlinefigure8loop.htm
Best regards,
David