Your return has two moving parts
A U.S. investor's result combines the stock return in won and the change in KRW against the dollar. A rising stock can still produce a weaker dollar return if the won depreciates enough.
Use the same time window
Compare the equity purchase and sale with USD/KRW over identical dates.
- A higher USD/KRW rate means one dollar buys more won—usually a weaker won.
- Dividends are also converted back into dollars.
- Hedging changes cost and risk; it does not eliminate every basis difference.