I tested both the Jo-Ann fabric grosgrain ribbon and my homemade silnylon loops sewn to a 1/2 inch rolled silnylon tarp hem in various configurations. Here is what I tested and the results.
I started with this silnylon loop sewn on with two Xbox stitches. This loop failed when the regular strength Polyester Gutermann thread broke on one of the Xboxes. It did not come close to holding my bodyweight. Two other things I noticed about this configuration were: it put a lot of stress on the hem seam, and it pulled on one side because the loop ends were sewn on one side.
Next I tried this loop configuration with the loop ends sewn on each side to give an even pull, the loop ends sewn over both the hem edge and the regular tarp fabric with a reinforcement patch sewn on.
This worked better than my first configuration. It was stronger, but did not hold my body weight. Again the Gutermann regular strength thread was what failed first, along with the tarp fabric ripping out. It was a balanced pull but very concentrated.
Keeping the loops sewn to either side, and the loops sewn over the tarp hem, I abandoned the reinforcement and tried the following configurations, this time with grosgrain.
Spreading out the loop ends was better than keeping them together. Putting one loop end on either side made for a nice even pull. Sewing the ends over the tarp hem kept pressure off the seam but still seemed to utilized the extra strength of the tarp hem. The weak link was the single layer thin grosgrain ribbon and the stitching. The stitching being the weakest.
The next test I upgraded the stitching. I used extra strength Gutermann polyester thread bought from Jo-Ann fabrics. It is the black thread in the picture. The grey is regular strength Gutermann. The extra strength Gutermann was much stronger. I could not make the stitching rip out under my body weight either in the regular XBox or Boxed Xbox configuration. The tarp fabric and the grosgrain were now the weak links. One of those grosgrain loops held my body weight before the tarp fabric ripped out - not along the hem seam.
Lastly, I tried a homemade silnylon loop sewn with one end on each side of the tarp with the ends spread apart and secured with one large Xbox made from extra strength Gutermann.
With this configuration the silnylon loop and thread is plenty strong, configuration of the attachment makes for a nice balanced even pull on the fabric and takes advantage of the hem strength but does not put extra stress on the hem seam.
I like this loop setup the best from my testing.