I appreciate your comments but I think a statistically significant finding in test 1 certainly reaches the goal of a demonstrable audible sound difference.
Some here may not know but several commonly available mic reach up to 40khz. The increasing adoption of hirez in the pro world has created demand and mic technology continues to improve. Several omnis and ribbon mics have these stats.
Damage to human hearing by airborne sound of very high frequency or ultrasonic frequency: HSE report 343/2001.
Lawton reviews 40+ years of research on the effects of high frequency sounds which while not consciously detectable can cause discomfort, headaches, nausea and vomiting. Since the tests where the 2 subjects detected a difference had the longest exposure they would be most likely to generate these "discomforts" while the shorter exposures would not. This would explain the paradox where the shorter test was less sensitive than the longer test which is not normally true.