Batten tension is not as important and batten stiffness
and taper.

When you over tension your battens, you do induce a
deeper shape. However, it is concentrated at the batten
pockets. Very soon you will have a scalloped sail that
is probably not going to be very fast. The sail shape
is what it is. Match your battens to that, generally speaking.

Experiment with very stiff battens (top third of sail)if you like.
Google RBS Battens to find some material to use. Experiment with
untapered and battens that are very flexible at the forward
third, too. You will be able to see when a batten is
not conforming to the shape of your sail (as cut), and
the effect that stiffer battens have on setting it
up for a flatter or fuller shape. The battens lower
down tend to be overpowered by the sail itself and
you will find little to work with there. The top battens
support the sail leech, however, and it's a whole
different ball game.

Attempting to do it with tension is not the way to go.