Is the form stability of the foil a major reason why the TR-1 and TR-2 have 9 battens vs some of the other brands that have only 7 on their smaller slalom sizes?

Yes. more battens is one part of it. But the most necessary thing is shaping of the body and luff panels that "forms" the profile under tension. You need to have sufficient broad seaming, whether vertical or horizontal, to maintain the shape under great tension. That also locks the draft in the right place and doesn't let it shift around when the rig loads. We are learning more and more every year how much shape it takes and where to put it. I would suppose that with today's computer technology you could do finite element modeling to show how much 'shape' you would have to put in to keep the shape under load, but so far i haven't heard of anyone doing this because there are so many other considerations to figure in, like sideways bend under load and the fact that there are unpredictable things like patch structures and webbing attachments. I expect that our practical experience is working pretty well.  more