Well I would first determin if the player position is greater than the bottom of the platform, meaning he is below it, or above the top of the platform, meaning he is above it. Also you should detect if the player is to one of the sides of the platform. If you get that going you'll be some steps closer to perfercting it, but as for the jutting up and down I'm not sure yet, the PMO in my experiance has never been good with moving obsticles or un natural shapes... hmmmmmmm...