In currency hedging, when foreign currency’s spot rate > future rate, downward sloping, it will lead to a negative roll yield. When foreign currency’s spot rate < future rate, upward sloping, it will lead to a positive roll yield.
What’s the logic? If foreign currency’s spot rate > future rate, downward sloping, the currency will depreciate, a short position shouldn’t have a positive return? Why there will be a negative roll yield?
You are associating falling/rising FX rates with depreciating/appreciating currency, when in fact it is the opposite.
If (Spot FX rate) < (Future FX rate) that means (spot value of currency) > (future value of currency), so rising FX rate means the currency is depreciating and it will lead to positive roll yield as in case with commodities.
When Fp/b > Sp/b then in the future base currency will appreciate in terms of price currency. This would give you upward slopping curve( means contango). If you have long position in b, you will have -ve roll yield (same logic as commodity).
You got it the other way round, if the future rate < spot rate, you have a positive roll yield. If the roll yield is positive, then the pricing currency should appreciate. In this case, you hedge to lock in your profit, unless you expect it to appreciate more than implied by the futures price.