The major losses are not in the DC-AC conversion nor in the AC-DC conversion. Both are usually done with high efficiency. The losses are in bridging the 1 mm air gap between the transmitting coil and the receiving coil and the presence of any other conducting material nearby. You see when the Qi charger (or whatever tech) transmits it's power over that gap some of it leaks out through the side. That leaking field starts to induce current in whatever conducting material it encounters. Those are your losses and they scale up with something like the third or fourth power of the distance between the emitting and the receiving coils.
By the way, the recieving end of OpenDots treats the power as AC, as it feeds it through a similar rectifier, in order to correct for polarity changes. These losses are not removed.
The are not a simple percentile loss however. On high power installations (like car charger) this rectifier would not be a simple Shotkey diode rectifier. It would be a sensing circuit with mosfets to switch the connections. Those are more expensive and have make no sense in low power applications but for the charging of a car using a mosfet rectifier makes sense.
You see, even Shotkey diodes have a 0.2V voltage drop over them. With a 40A charging current this means 8 W is continuously turned into heat by the diodes. The mosfet rectifier needs some power to work but that is in the order of 0.1 W, depending on the number of contact points.