Among the proposed interface circuits for Piezoelectric energy harvesting (PEH), Synchronized Switch Harvesting on Capacitor (SSHC) rectifier distinguishes itself since it achieves high power efficiency while requires no inductor. The power SSHC can extract is a function of the voltage flip efficiency. In previous studies the flip efficiency is given only under particular condition. This paper presents the derivation of a generic flip efficiency expression. From the result, a novel capacitor-scaling design is proposed which can reduce the total switched capacitance by up to 50% while achieving the same performance (or to enhance performance while maintaining the total capacitance).