The exhaust remains at frame level. The fuel line is entirely above frame level, against the body floor until it reaches the inner wheel well and turns downward. They never come close to one another. The pictures I posted above show the entire run, from tank to union. They overlap. If you study them you will eventually get it.
Another way to think about it is that at the factory the tank and rear line stayed with the body. The line remained clipped its entire run to the body. The forward line remains with the frame, clipped to it for the entire run. Once they are mated, the union is mated too.