In the upper panel, the relative amplitude of the low frequency to the high frequency e₂ modulations (Θ), see main text for definition, is plotted vs. the mass of the perturber. The higher Θ, the higher is the probability to detect the long-term modulation of the eccentricity. To show the effect on the shape of the resulting e₂ modulation, three extreme cases are presented in the bottom panels: 1) a low-mass solution, with M₃ = 2   M_J and P₃/P₂ = 23; 2) the solution with maximum eccentricity amplitude, with M₃ = 48   M_J and P₃/P₂ = 13.4; 3) a high-mass solution, with M₃ = 152   M_J and P₃/P₂ = 36.