Does it matter if you draw the ENDS tighter, using the shockcord vs. attaching shock cord to the SIDES and running over the ridgline....or should you do both.
With the full length incubator (rated for 20 degrees) I found my back was chilly at 33 degrees. Cool enough to keep waking me up. The ends of the underquilt are snug against the hammock and I have a shockcord connected to two loops on each side of the quilt and running over the ridgeline, which should be keeping it snug against the hammock.
I was wearing smartwool thermals, shorts, a long sleeve tee, wool socks, and a fleece hat.
My top sleeping bag was more than adequate but my back stayed cool.
I don't think there's any reason the 20 degree full length incubator shouldn't keep me comfortable down to freezing, and below.