IIRC the rear end of the midships pipe hangs from the two donuts and so rotating it does affect how it centers on those donuts. But you're right - it has little effect on lowering it. I think I found that by slightly rotating the over the axle pipe (I would say counterclockwise viewing from the rear of the car) it tends to pull the rear of the midships pipe down from the floor. I think it also messes with the centering on the donuts in order to lower it from the floor. The other limiting factor (failing memory) had to do with what it does to the rear muffler - too much rotation one way and it hits the gas tank - too much the other was and there's interference somewhere else. My happy medium, with no knocking on the floor and no knocking on the gas tank meant that the center donuts were unequally loaded.
hope this helps.