I have only used the ripstop from JoAnn and Hancock Fabrics and have never had an issue. I can see small pinholes in one of mine that i have used over twenty times now though. That one has been through the ringer with no failures thus far.
The shoulder squeeze (cocoon) you mentioned might be due to the short hanging span.
Another thing you might want to look into is a ridge line. Good job though, you're on the right track!
It's a hammock thing, you won't understand!
The wife no longer kicks me out of bed after she saw a hammock hanging in the dog house.