Originally Posted by odds
Not sure what you mean by there is no difference. On a whoopie sling, both ends of the constrictor are under tension. On a UCR only one end of the constrictor is under tension leaving the other susceptible to slipping.
What I mean is that if you disconnect the fixed-loop end of the whoopie from the load and instead connect the free end (the end normally pulled on to tighten) to the load, then you have a UCR (which can extend further than the whoopie configuration).