every aftermarket bumper is designed to look lower than stock. My dad got a new front bumper for his SUpra and it was roughly an inch to three inches lower than the stock side skirts or rear bumper. That's why it's always in best interest to purchase complete kits due to the kits low look is universal.
My car looks fine with the Euro RS "Collection" bumper and stock S2 (which are the same size as regular ZX3) sideskirts. It actually sits even now, rather than the front looking a little higher like it did with the normal front.