Hubcentric wheels/rings/spacers fit securely to the hub. That way force can be passed through the hub, and the whole assembly fits very tightly together so that it's aligned properly when you put it together. Lugcentric setups ( I think the Miata is one, but I'm not sure) rely on thw lugs only - there's no contact between the hub and wheel.
At first, it would seem that hubcentric is the way to go: after all, the lugs are pretty small to take that kind of force. However, it's not the lugs that take the force. The lugs are in tenion, and they hold the wheel to the hub tighly enough that the friction between the wheel/hub keeps the car up and off the lugs/hub center. So really, the difference between lugcentric/hubcentric is not that huge. The force shouldn't go through the hub anyway. Now for spacers, I'd go hubcentric anyway, partly because you're adding leverage and stress to the system, and partly because it's easier to get it centered. A poor-fitting spacer can throw off your balance and also not seat properly.
This is a pretty rough write-up, some googling will get you more technical answers.
Last thing you need is your studs breaking.