You don't want "symmetrical" you want "toe in" ie. the front part of the pad contacts the rim slightly before the rear. If your pads/brake arms are adjustable, you can achieve this by loosening the pads, slipping a couple of business cards between the rear of the pads and the rim, squeezing the brake lever, and tightening the bolt. If they are not adjustable, you bend the arms slightly with a monkey wrench.
Paint/powdercoat on rims, BTW, is stupid. It will cause lousy braking until it wears off, at which point it will just look like hell. And for all I know, it could be responsible for the squeal, too. Unless fashion trumps function in your book, you should ditch it.