Two economies with different uncertainty will not scale

“How Are Uncertainty and the Uncovered Interest Parity Condition Related?”

Sort of the definition of comparative advantage. The exporter with a local surplus of a good will contract to ship it out before the futures market can react.  The exporter/importers have the inside information in this case, not the currency market.

But the inventory cycles are altered between the two economies because the uncertainty is a Nash equilibriating variable.. Any price comparison will not hold for longer than the same price comparison with a single monetary zone.   One has to believe Uncle Milts pluck theorem.  

It is in general going to be nearly impossible to predict future currency prices unless one side or the other has foul central banking.  The classic case is oil prices are inverted from dollar value, for obvious reasons.  That means oil exporters will be trading against the US safe rate, removing most of the hedge from the currency markets. OPEC economies scale as oil production scales, and that has been much different than how the USA economy scales, so OPEC has to set side reserves in Treasury bonds to carry them over during pluck periods. Part of oil exporting is emulating the yield curve of the trade partner. So OPEC constantly removes currency hedges with oil importers, mostly the USA and China. generating the Fama puzzle.

Japan has low market uncertainty internal, it can fire up the assembly lines in response to any foreign goods shortage, rarely runs out of intermediate inventory, this is a high rank economy, in sandbox terms. Oil economies would be of higher uncertainty, low rank economies.  One can say the Japanese economy is more accurate, it can describe both the OPEC economies and the US economy. It is a trading and manufacturing economy. So Japanese traders will have the inside track on currency shifts many times.

Call it the Baumol process. The Japanese economy can absorb a disruption in OPEC with lower volatility than can the USA.