Are some of the posts for the shock ends threaded all the way in. I am going to check the front on ours and see if that is the case it could be mine are too tight. They are double nutted on the bottom and I doubt it came like that. That could be my problem.
Usually the posts for the shocks have a collar where the thread ends and you bottom out a jam nut holding it on, right?
Dale the radius rods hold it back some, the 5th bar the most. It can only travel as long as the radius rods and as the side way "5th one" drops it will start to pull it one way the more the axle drops. Then there is only minimal "twist" in the other four, it will stop itself somewhere. I suppose the more the rod bushings are wore out the lower it will drop. If that happens before the shock fully extends is the question.
I have seen air ride trlrs with a strap around the axle housing limiting its travel. Possibly to keep from snapping shocks by overextending.
When I get the front apart on ours I will see if the axle will drop past the point where the shocks are extended out all the way. All that will be holding it will be the radius rods and a jack.