if you notice in the pics, one of the reasons i sold my sil micro, is there is no sewn ridge seam. the ridge can tend to get a little flappy, and the cat cut isn't as integral. that and i wanted a bigger tarp to hang out under if and when getting rained on all weekend out this way.
cannibals, built in spinnUL, does have a ridge seam due to the limited width inherent in the textile. he reports it pitches nice and tight, with a crisp cat cut ridgeline.