Modelled visibilities of the 2.2 μm continuum emission as function of baseline assuming a single disc brightness distribution overplotted with the observed ones as obtained with GRAVITY for (a) G034.8211, (b) G301.8147, and (c) G287.3816 as fitted using LITpro (Sect. 3.1). (d, e) Same as before but for observations obtained with AMBER towards G233 and G231, after fitting a Gaussian, a uniform disc, and a ring. The background flux contribution is found to be 16% for G233 and ~9% for G231.