How Do I Change Gears?

Bending the mast is the main mechanism to flatten a mainsail.
Its not just bending the mast that matters. It needs to bend by the right amount, in the right places at the right time.
The effect of rig tension on mast bend will depend on spreader configurations AND the relative position of the shroud bases.
The mast needs to bend to suit the luff round cut into the mainsail for the sail to perform as intended.
As wind increases we aim to flatten the top of a sail first so we should bend the top of the mast first.