On my Hobie Cat 14, I noticed that the main halyard can be locked to its hook in 2 different positions which are far from each other about 20 cm. I have also noticed that the main in its tack corner has two holes which happens to be far from each other about 20 cm again (the second hole is 20 cm over the usual one on the tack following the luff).
Is this perhaps intended to reduce the main size? If yes, how? (I mean, do I have to roll the main around the boom?) If not, what are they intended for?