Notice that my simulation gives average Watt readings.
.124 at the power source.
.092 at the load.
Efficiency calculates as .092/.124.
To produce a graph of efficiency vs input impedance, change the 50 ohms to a variety of values and run simulations.
Then for each run, one way or another, you must find the average Watts drawn from your power source.
Either:
a) the simulator does this for you (like Falstad's which I use), or
b) you must attach components that perform averaging, or
c) you must hand-calculate the area under the curve of an entire cycle, or
d) find Amperes (rms), and multiply by supply Vrms.