Following on that, it's been stated here many times before, but bears repeating and directly follows from the above, that just as an omnidirectional-pattern microphone no longer operates in a fully omnidirectional way across the full frequency range when used in this manner- becoming much more pseudo-cardioid-like at upper-mid and higher high frequencies due to the acoustic shadowing of the close object - similar altercations happen with directional pattern microphones used this way. Actually, the effect is somewhat less predictable and more complex than with omnis due to omnis lacking rear vent access paths to the back side of the diaphragm which directional pattern microphones employ, and all the complications that come with that whenever the microphone is not immediately surrounded by free space.
A practical implication of this when making comparisons between the two pairs is be to shoot for precisely duplicating the arrangement of the two microphone pairs as closely as possible, not only in terms of the spacing and angle relationship between the pair but also in terms of the position of the pair in relation to the solid object that is in extremely close proximity, partly so that the external influence of that solid object will be as similar as possible in both setups. Wearing them just a bit further forward or back, up or down, or closer or farther from the surface can make an audible difference. When listening specifically for this effect, listen to the effect on off-axis and diffuse/reverberant sound as well as the direct-arriving sound of primary interest.
Beyond minimizing variables for comparison purposes, this kind of setup consistency in achieving good repeatability of the configuration will also be beneficial in terms of achieving good consistent repeatability of response in regular use, night to night .