Bubble plot of every Lorentzian in each HID region (vertical axis) of Cygnus X-1 as a function of their characteristic frequency (horizontal axis). The area of each bubble is proportional to the covariance rms amplitude of the Lorentzian. The colour scheme indicates the corresponding phase lag. The diamond marker highlights the narrow QPO responsible for the sharp coherence drop, which becomes apparent in Zones 3 to 8, corresponding to intermediate states with 1.8 < Γ < 2.4.