Just added CRLs to both my tarps, one above and one below. All testing thus far shows both to be very effective, neither seems easier to set up/take down than the other, and neither seem to put any noticeable excess stress on the tarps. From my limited experience, I say pick whichever works for you and run with it. I did have a few crafty veterans here tell me that if the ridge seam of the tarp has catenary cuts, go above.
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