It's far from simple. In the upper sections, leech control is critical
to determine how much draft is right. As wind velocities at the top are
higher and if angles of attack are set to be optimal by twist control
then the upper secion should be slightly flatter. This is possible
enitirely due to the stiffness of modern fabrics that will properly
support their leech as the wind pressure increases. Have a look at the
North web site for some photos of their racing sails and try to find
full upper sections.

Cheers MC

DSK wrote:

It is the simple fact that a well cut sail will be
relatively deeper in the upper sections.