The portion of the mast above the diamonds does not have diamonds to force it to bend on its long axis. Naturally, it will bend on its short axis.

Rotate the mast to allow the sailcloth's tension to bias the bend in one direction (sideways bend) rather than to have the sailcloth's tension pulling straight down without any bias to one side or the other which, results in an "S" shaped bend.

In short, rotate your mast a little bit more and you will see the top section take shape in a "(" shaped curve rather than in an "S" shaped curve.

GARY