if you're only goal is to match the mast to the sail with the diamonds, then why do you tension the diamonds on big air days and ease on light air days? Oh yeah, it's to bend or straighten the mast....... Trust me on this, you can get a sail MUCH flatter with less downhaul/cunningham by prebending the mast.

Especially with a boat like the I20, the increased diamond tension makes a big difference in flattening the sail when it's windy.

Yes, the mast bends a little differently but the overall effect is the same, open leach. Additionally, by tensioning the diamonds you get more stability in the mast and will keep the slot more open.