Various aspects of eCB-SMBH detectability with GRAVITY+. (a) Flux ratios of the NIR emission originating in a dust ring with respect to the optical continuum as a function of h (dust-ring dimension), for different photo-centre displacements, shown as black lines. The GRAVITY approximate detection limit at λ_lim ~ 1.95 μm in terms of the flux ratio for dust emission arising at different distances and observed at 2.2 μas is shown as a blue curve. The shape of the blue curve depends on which power index of h is chosen; here its value is set to –2. (b) Expected S/N for N_O = 0.25 and . (d) Expected S/N for N_O = 0.25 and . (c) Detection distance for different eCB-SMBH parameters and eccentricity e = 0.5. The crosses show the ten best GRAVITY+ targets (see Dexter et al. 2020), assuming a circular orbit.