Lots of SM guys and my RX7 has it mounted on the right side of the main hoop just inside the window.

A Miata is small enough that most people can reach it in that location while belted in.

I can't reach it in my RX while belted in, but it's easy to see and access by corner workers-- assuming you're not on your side against a tire wall. I plan to relocate mine to a more easily reachable location- maybe just farther inside the cage- because this car is wired such that gauges and some 'other stuff' are active as soon as the switch is turned on. Maybe I should just fix that part.. lots of little things on this new car that I'd do differently.