When expected returns have been realized within a specific time period, it seems reasonable to assume that R2 would have been rising and elevated above at least 62%.

As a cycle and or direction changes, the explanatory power of the result of the previous directional trend will decrease as another direction may be taking place.

From my observation, I see the decline in R2 as an opportunity to enter trades where the expected return is high and exit trades when the expected return has expired which may include an elevated R2.

From my own study, R2 must be used together with one or more indicators (type: price, oscillator, valuation, RSI, etc) where actions are coincident with the other indicators.