[yetanotherphd]

I was implying that when I said "countries in the world that are big enough to have their independent macroeconomic policy", but that was somewhat glossing over the issues you've raised.

I'm not a macro expert, but my understanding is that a country need not be completely autonomous in order to have its own macro policy. Goods cannot flow perfectly between countries, and so macro policy will always have some effect.

The more a country imports and exports, and the smaller the country, the less impact its macro policy will have.

So the reserve bank of China can influence Chinese interest rates and hence have an impact on the Chinese economy. On the other hand the reserve bank of a "small open economy" cannot do much to change interest rates.