No i haven't made it or tested it but then you were the one that said that it was a figure eight to make it easy to un-tie but now you're not untying it. I'm confused and will just leave you be, I think.
I don't want you to be confused, So I will try to explain myself a bit better, so read the first post (how to tie) again and then try and make the buckle loop, don't worry about the other bits for now.
Then in the last picture you see how the prong is threaded through the loop, use your finger to create the eyelet that would be in the Tarp.
Pull on the loop as if tension was applied and you will see that it does not come undone because the stopper knot will not allow the loop to loosen round your finger.
The idea is that once you have tied the buckle loop, it stays tied and on the end of your guyline. It takes place of the carabiner you may use to connect a guyline to a eyelet.
The only reason for the knots being able to be easily untied is so sometime in the future you may want to untie the buckle loop for whatever reason you can do that easier without the single overhands being locked tight and very fiddly and irritating to undo.
I hope that helps, and I will add some more pics for easier initial tying. Please let me know it if doesn't make sense and I will try and explain further. I don't really have the tools to make an instructional video.
sorry the forum won't let me set spacing so all the text is bunched up.