Positions of the n = 1 peaks for all the possible emission configurations in the case of a Schwarzschild black hole (green), a RZ black hole with non-vanishing parameter b₁ = 0.1 (blue), and a RZ black hole with non-vanishing parameters a₀,  b₀ = 10⁻⁴ (yellow) or a₀,  b₀ = 0.1 (red). Dashed lines represent critical curves: the green and blue ones are superposed while the yellow one is slightly above them.