Left panel—[η/ϵ − f] parameter space for FRIs, FRII-LERGs and FRII-HERGs with z > 0.05. The curves are obtained via Equation (2) by assuming the average L_{[O III]} and L_NVSS luminosities (and standard deviation σ) in Table 2. Dotted lines correspond to 1σ uncertainty. The separation at ﹩\mathrm{Log}({L}_{[{\rm{O}}{\rm\small{III}}]}/{L}_{\mathrm{Edd}})=-6.7﹩ between HERGs and LERGs is based on Figure 4. The intersections of the horizontal line with the curves mark the f values required to have the same efficiency ratio (η/ϵ = 0.98 in this case) in each class. Right panel—same plot for FR0s, small FRIs, and FRIs with z ≤ 0.05. The horizontal line corresponds to η/ϵ = 0.49. The vertical arrows indicate that the η/ϵ values traced by the curves have to be intended as upper limits.