Since I have made a hammock stand that is only 11' long, I cannot use the whoopie slings I've made for the trees. My question is how short of a WS can be used and still be safe? My concern is the WS works by the constriction of the outer rope over the inner rope. At some point in making a short bury, there will not be enough outer rope to make purchase on the inner. Has anyone experimented with this?