We have no proof JR worked on it. We have only his word. FW would have seen him do it. We all have our thoughts about why FW has not spoken more about whether he saw JR do the things he said he did, but none the less, he has not corroborated any of it. A slip knot doesn't move by itself, it has to be pulled. The distance between her hands is what is important, more so than the distance between the loops. The position of her hands, set by rigor, show that her hands were not pulled together, or they would still have been together, even if both wrist loops were removed. JR said her hands were tightly bound. Yet we know that was not the case because if it were, her hands would have been together even if JR removed the ligatures, and there are no ligature marks on her wrists.
If there is a distance between the loops that matches the distance between her hands, that would be an indication that the loops were put on her after rigor had fixed her arms in that position. Isn't it a shame no one ever measured to determine this?