I first tried using the cord/rope setup like you describe. It didn't work that well for me. It seemed that with a very short piece of shock cord, I was having to pull it very very tight to get the overall snugging effect that I wanted.
I then switched to full length shock cord and have had much better success.
One item to note is that my winter UQ is very wide, so that may have some affect. This probably requires a little more stretch of the edge of the UQ during the entry/exit of the hammock that made the short shock cords more of an issue.