I understand what you are saying and have had the same experiences
with certain ropes. What I am trying to point out is that with a
slippery bowline, I have noticed that a minor detail in how you insert
the last piece of rope into the loop can play a huge part in how
difficult it is to release.
Whether that little detail has anything to do with what you are doing
and if it does, whether it is enough help, is another matter. It
seemed to make that type of difference for the small diameter
spyderline I currently have for the few times I have played with it.
A slippery bowline by itself should be all you need to finish off a
hammock suspension line unless you are trying to tie it off taut and
is reasonable to tie and release when it works right. Whether it
works right is a function of several things. The materials involved
AND how you insert that last piece of rope in the loop are a couple of
those things. If you are trying to tie off a hammock suspension line
taut, I would suggest you consider tying it off higher on the trees so
you don't have to do that. I think tying off higher with some some
initial sag is best approach when the distance between trees isn't too
large to prevent it. There is less stress on everything that way and
you get less stretch when you get into your hammock as well.
When we hang a hammock, the first thing to determine is the span, or
the distance between trees. Once we do that we decided how high to
tie off the hammock. My suggestion for most hammocks is to tie off
shoulder high for spans of 12 feet, head high for spans of 15 feet,
and as high as you can reach for spans of 18 feet or more. When you
do that you should have some sag in the hammock suspension so the
hammock itself drops to a usable distance above the terrain. With sag
in the suspension line you don't need a trucker's hitch to pull the
suspension line taut and the slippery bowline will work by itself.