how much tension on the sailbattens

I first time removed the sailbattens this last winter.

Now my curiosity has been arroused. Last year I broke the top two battons on my main in the only race I participated in last year. I have the new battons but unfortunately do not know the exact size. Since each fiberglass batton splintered, I had to cut them in parts to remove them last winter. I have new stock to replace these within the next couple of weeks. I was planning to cut the length close and adjust to a snug fit using the provided set screw. Not to open an unended physics discussion here, how should the tension be set on these battons? Does this significently affect the performance of the sail if not adjusted correctly?

My experience has been that you must have very little tension on the top 2 battens in light air.  Otherwise the batten will not bend in the opposite direction when you tack.  This means only 2-3 turns of the set screw at most. Since I'm always concerned about losing parts for which I have no replacements, I just had my sailmaker get me 2 extras of each size set screw from Bainbridge.  Let me know if you need the measurements of the top 2 battens.  My main is off and I can measure them later this week.