Mike, thanks a lot for your reply. Now I see that the petal shape
spreads diffraction pattern, making its peaks lower.

BTW, this whole project, as proposed by prof. Cash, probably won't
work, because the Sun light spread in all directions from the edges of
the occulter will totally dim out the light from the remote planet. So
to make the whole thing work, one will need a huge screen (a few 100s
m in diamater) independently floating in several km from the occulter.
While it is feasible, it will enourmously increase the price tag.

And if they're going to place it at a Lagrange point, in 1.5 Mkm from
the Earth, they will need the 2nd screen to protect from Earth
reflected light. And then the 3d one, for the Moon light...