A microphone's polar pattern is non-uniform front-to-back, making rear-pointing feedback tests inaccurate

A common stage-monitor feedback test technique is to point a microphone toward its monitor from the rear (using a mic stand pointed backward). This is inaccurate because cardioid and supercardioid microphones have different sensitivity patterns at the front and the rear: the rejection notch, sensitivity roll-off, and coloration at the rear differ substantially from the on-axis front response. A test conducted from the rear does not simulate the actual feedback path (front/side of mic → monitor → front/side of mic). Engineers who test from the rear may notch frequencies that are not actually problematic on-axis, and miss true feedback frequencies.

Examples

A Shure SM58 has a cardioid polar pattern with significant rear rejection and altered frequency response off-axis. Pointing it directly at a monitor from behind gives a different ‘feedback frequency’ than what would occur during actual use, where the mic is held at the front with the monitor behind.

Assessment

A stagehand tests monitor feedback by pointing a vocal mic directly at the monitor from the back. What is the technical flaw in this test? Describe a more accurate alternative.