Based on past experience, an effective way to gradually reduce the balance sheet to a more efficient level is to change that reinvestment policy to limit, or cease, reinvestment. Allowing this “runoff” was the main way the FOMC shrank the balance sheet before the pandemic.
I expect the reinvestment strategy will be heavily influenced by the Fed’s experience with this policy between 2017 and 2019. During that time, the FOMC recognized that the monthly maturity of securities was lumpy; some months there were many securities maturing, and others few.