[tenuki]

oh, and the reason it's bad for your spreaders to creep up is that once they get high enough the loads start changing from pure compressive to lateral and will bend that spreader the rest of the way up like a twig for the same reasons I described above. They wouldn't creep up under tension, since a small component of the force under tension pushes them down, but as G said, if they are loose on the lee side they can creep up.