Well that sucks, at least spacers are well understood, just keep them to a minimum thickness needed to clear the caliper and all should be golden. Interesting that it was making contact with a 45mm offset? Possible that the Miata site I was looking up the info had a typo, that or the spokes have a lot more curvature than normal. I take it clearance is good around the struts/spring?
I bought some 1/4inch spacers and that was way more than I needed. I need some that are about 3mm thick but I can't find them.