If I understand the scheme above, the arrangement is illustrated by the attachment, yellow lines being the tarp lines.
If that's true, then the only difference between this and tieing the tarp to the prussik lines is that the tarp is positioned lower---it is equivalent to tieing off the tarp lines to the rings. The tension on the tarp line will decrease when you get in, just as it does if you use the prussiks w/o rings.
Now pre-tensioning can help as BillyBob pointed out after reading the instruction manual, and having the tarp lower may be a good thing. But I don't think this will work in the same way as the original idea, which will I'm pretty sure tighten the tarp line.
time for my complimentary bowl of cheerios...