Although the duplexer in a full-duplex transceiver circuit may only be guaranteed by the duplexer manufacturer to have a transmit band rejection from its TX port to its RX port of a certain amount, and may only be guaranteed to have a receive band rejection of another amount, the actual transmit band rejection and the actual receive band rejection of a particular instance of the duplexer may be better than specified. Rather than consuming excess power in the receiver and/or transmitter in order to meet performance requirements assuming the duplexer only performs as well as specified, the duplexer's in-circuit performance is measured as part of a transmitter-to-receiver isolation determination. Transmitter and/or receiver power settings are reduced where possible to take advantage of the measured better-than-specified in-circuit duplexer performance, while still meeting transceiver performance requirements. Power settings are not changed during normal transmit and receive mode operation.