I agree with these suggestions. A good portion of the hi-hat sound is the stick definition, which would be mostly lost by miking underneath. It could be that the Shure mic you're using just has lousy rear rejection, so trying a different mic may solve much of your problem. 414's and 451's have excellent rejection, as do small Neumanns like KM184's---which have the added benefit of a very smooth off-axis response. Recently I've been trying a suggestion from an interview I read, and miking the hat about four inches past the edge, pointing slightly away from the kit and essentially at the floor, and I've never gotten a more silky, sizzly sound. (be sure to keep the capsule above the plane of the cymbals to avoid air puffs) Great for fusion/jazz, at least.