Simulation of photo-centres for continuum source (blue dots), emission line (red dots), and relative positions (green dots) of emission line photo-centre with respect to the continuum photo-centre. The binary system parameters are: M₁ = 6 × 10⁷ M_⊙, M₂ = 4 × 10⁷ M_⊙, e = 0.5, Ω₁ = 180°, Ω₂ = 100°, ω₁ = 0.1°, ω₂ = 180.1°, R_sub = 150 ld. The mean mutual distance of the components is 100 ld, the binary distance is ~700 Mpc, and the observer position angle is 40°. The emission line source is located in the BLR that is bound to the primary, whereas the continuum is defined as the barycentre of the dust ring arc that is bound to the secondary and split by the CBD. The cross represents the barycentre of the eCB-SMBH.