Some have claimed that slightly beyond 'full open' offers a few more rpm...never tried it. The engine will respond pretty softly to small changes in disc position the closer you get to wide open anyway, so get it close by eye, and you should be fine. The important thing is that you have it closing the proper direction, otherwise the disc valve will not seat properly or idle correctly....etc. After a while, and some vibration, the disc will no longer fit correctly and you could see trouble even if rotated to operate in the correct direction.