Top: three telescope configurations picked for the example and corresponding to the positions of three of the VLTI UTs. Bottom: value of the kernel null as a function of the relative position of a source of unit contrast at 3.6 μm, normalized to the throughput of one aperture. The map is relevant for a target observed at Zenith and would evolve with the projected aperture map. The nature of the response is antisymmetric, as demonstrated in Sect. 3.3.