Mean (lines) and upper 1−σ envelope (shaded area) of power spectra from 100 000 simulated curves for different (v_e, R₀) configurations, in the absence of reverberation (F_BLR = 0 in Eq. (3)), compared to the data (same as Fig. 4). Due to the logarithmic scale, the lower envelopes extend almost to the x-axis and are not displayed for clarity. The vertical dashed line marks the boundary between low and high frequency.