I disagree- usually a short fit will result in pain higher up in the back/shoulders because you have to roll the back to fit in the cockpit and also is often accompanied by pain in the wrist because the weight is balanced to far forward on the bars.

When the reach is too long you wind up with too much weight balanced on the saddle and not enough on the bars. The lower back starts to hurt because it is taking the extra weight (that should be on the bars) and tries to move forward by flexing in a "u" type fashion