Is it a Cap or a Simulator? Rear Wheel Simulator would be dished IN. A Cap would be dished OUT, like a Front Wheel.
How is it secured to the wheel? We have the popular VersaLiner Simulators. Six of the "lug nuts" on each one are fake. Two are real and tighten onto the tips of two lugs. I put electrical tape in a crosswise pattern surrounding the two holes that actually tighten. Then I found I had to snug the nuts more than the little tool that comes with the Liners. I use a socket wrench. This quieted a squeaky rear wheel liner. Hard to believe but those big heavy wheels flex as we drive.