Just a word of caution on this. I think what you seem to be calculating is the centre of area. On an IOM where you are essentially dealing with a one design rig, and within the sail plan, most of the sail cuts are not far off standard - because of the requirement for them to be suitable for use in under and overpowered conditions - you can in practice use this as a datum point for comparing and setting up boats. But it is not the same thing as a centre of effort. In a sense there isn't really one. You would really need a series of complex iterations, first the centre of area, then the pressure distribution, then the shear twist, self induced twist and associated couples. Don't even bother to go past the first to trim up your IOM, but watch out if trying to directly apply the numbers you get to less rigidly controlled boats.
