The very first junksail I had was flat (Malena 1990). When I added four hinges in each batten (1991), the performance was much improved, but the weather helm also rose quite a bit.
I guessed the reason for this was that the camber was symmetrical, with the max camber midway between luff and leech (see NL 24, p.22)). However, when having another look at this photo, below (1992), I see that I have gone far to shift the sail aft about 20 – 25cm. I therefore guess now that the increased weather helm is a result of a combination of the two reasons; camber and sail position.
When I later made a new sail for Malena with cambered/baggy panels and with about the same sailplan as before, I placed the max camber point about 35% from the luff. This resulted in that the CP moved forward (see NL 30, p.21), giving very light steering.
Conclusion: The resulting position of the CP of your hinged sail will depend on where you place the max camber point.
I could be wrong, of course.
Good luck,
Arne
(click on photo to enlarge)