I have a Blackbird XLC and noticed that my winter top cover was sagging all of a sudden. Then I realized, I had just put my Cocoon over my hammock. I was leaving it unzipped just as an added underquilt for hanging in the yard at night. The Cocoon isn't as long as the XLC. I also didn't put the Cocoon under the ridgeline. Doing so would make the top cover useless. So I left it over the ridgeline at the ends and unzipped. It wasn't putting any stress on the cocoon zippers. But it was squeezing my ridgeline down closer and shorter causing the top cover not to be as tight. Acting like a stretched ridgeline.