In a wireless charging system, a power-transmitting node (TX) has a transmitter for transmitting power wirelessly to a power-receiving node (RX), and a signal receiver for receiving signals from the RX. During a power-transfer session, the TX accumulates data corresponding to its transmitted power level, detects an end of a received power (RP) packet from the RX, and then identifies a subset of the accumulated data. The TX calculates its transmitted power level using the subset of the accumulated data. The TX extracts a received power level of the RX from the received RP packet and compares its calculated transmitted power level with the RX's received power level to determine a presence of a foreign object. Accuracy of FO detection when packets from the RX are not properly received by the TX is improved.