Characteristic size of the emitting region as function of wavelength. The red points are derived from our MATISSE data. The 1.6 and 2.2 μm points come from PIONIER (Lazareff et al. 2017; Kluska et al. 2020) and GRAVITY (GRAVITY Collaboration 2019) observations, respectively. Black crosses represent our new fits to MIDI data published by Varga et al. (2018). The solid line is from the DIANA radiative transfer model of HD 163296 (Woitke et al. 2019). The dashed line corresponds to our flat diskmodel.