. . .
Test this on the beach next time you sail. Do some dry sailing. Turn the boat into the wind like it would be while sailing up wind. Sheet in, set downhaul, then set for lots of rotation . Then get behind the boat a ways so you can see the effect on the main. Now setup for minimum rotation. then check sail from behind the boat again or from which ever angle helps.

Easing the sheet will also give you a fuller sail.

You can also think of an airplane on takeoff with flaps down for a " fuller" wing.(more power/lift) As the speed of the plane increases the pilot " flattens" the wing (brings in the flaps)

Don't forget to adjust the downhaul as well.