Averaged differential visibility amplitude spectra (coloured) and the normalised Brγ spectrum (grey histogram) for IRAS 09149−6206. There is a clear positive differential visibility amplitude signal in the UT4−UT1 spectrum, which follows well the line profile. Solid and dashed black curves show the differential visibility amplitude of the best-fit BLR models (see Sect. 4.4). Several channels with large scatter at > 2.3 μm are masked for clarity. The same Brγ spectrum is displayed in all of the panels.