Radio-loudness parameters vs. Eddington ratios. Key as in Fig. 3: RL, blue filled circles; detected RI, red filled squares; undetected sources with ℛ^up.lim ∈ (1,10] , yellow open stars; RQ, green filled triangles; not classified, light-blue open circles. Undetected sources are also marked with small grey arrows. Only mean error bars are reported to avoid clutter. Big black arrows correspond to the upper limits found for the 11 X-ray non-detected sources in the “control sample”. The vertical dotted line marks the threshold of λ_Edd = 5, while the horizontal dashed line corresponds to ℛ = 1000.