I can hear 4Khz tones on a good day. I can also perceive small EQ changes that are done at frequencies above 10Khz.
But if you do the Klippel tests (you said you did right?), that it done blind, then how small such EQ changes would that be for it to be perceived? Just curious, that's all.
Our ear/brain connection is dependent on more than absolute frequency response.
On this point, we obviously have to agree because it is factual, 100% objective, but we also need to keep in mind that, there is accuracy/transparency, and preference. One being objective, the other subjective.
For accuracy/transparency, it is easy to agree that if the input signal waveform is the same as the output signal waveform, that accuracy is achieved, and if not then it is not 100% accurate by definition.
So, cutting out frequencies > 22,000 Hz should result in the output signal inherently more accurate for transparency than preserving it because any frequencies resulted back in the audible band of up to 20,000 Hz due to the frequencies in the >20,000 Hz ultrasonic range will be a result of distortions such as intermodulation distortions. Some people may be able to detect such distortions and prefer their presence, but it is doubtful, in the case of the likes of the high quality processors such as the AV10, because the magnitude of such distortions will be too loud for it to be in the so called audible threshold anyway.
The ringing, including the unnatural pre ringing of a linear phase filter vs the natural ringing of a minimum phase filter, will make a difference in perceived sound. Then, there are different amounts of delay and ringing with fast or slow filters. Some will hear it. Some will not. Some will care, some will not.
Their are sites that I know of, conducted blind listening tests on those effects, and if I remember right, most couldn't tell a difference while some could, though I don't recall any conclusions have been made so far.