I would assume that having the CPU heatsync 'sucking' air inwards which in turn is blowing it onto the metal conductor in which the fan is connected to would be the better way to have your heatsync setup. Having it blow outwards away from the metal would just continue to allow the metal conductor to stay very warm where as having it blow air onto the conductor will cool the metal before the heat has a chance to build up and spread to nearby components.
Think of it this way, when you have very hot food in your mouth, what do you find yourself doing to cool it off? Or hot food on a fork or spoon? You blow onto it to cool it down, not try and suck the heat away from it. That would just be less effective, not to mention make you look stupid .