I have got very similar result when measuring THD vs. power recently, please see attached.
Thank you for sharing. The measurements we did was THD + Noise so slightly different to your THD only measurements. Either way these amps are very good ;)
regards
David
You are right, I like the THD and N components being separated. In my case, noise is 36 uV with 20Hz-22kHz bandwidth unweighted. At higher power above some 10W, THD plot is almost identical with THD+N plot with this amplifier.
Also we use a filter to filter out any ultrasonic noise from class-D amps.
https://analog-precision.com/forum/performance-and-measurements-12/measurement-equipment-14/