The sound intensity technique used to determine directional information assumes the B-format microphone patterns are centred about the same precise point in space (are coincident).
For low frequencies, where the wavelength is much larger than the capsule spacing, the capsules appear to be coincident. However, as wavelength decreases the capsules become increasingly less coincident and the accuracy of directional accuracy reduces with increasing frequency. This becomes an issue above about 5 kHz for a TetraMic.
When Broadband or 1-8 kHz filters are selected in the IRIS plot, IRIS calculates directional information from B-format signals which have been low pass filtered at 5 kHz. Level is calculated from the original signals.
For horizontally arriving plane waves in a free field, it was found that IRIS with a TetraMic was generally accurate to within ±7.5°. More details are here.