Illustration of 8 configurations of azimuthal sectors. Forward and backward pseudorapidity windows of the width $\deta=0.2$ are additionally split into 8 azimuthal sectors with the width $\dphi$=$\pi$/4. The red sectors correspond to the first window of the FB pair, the green sectors to the second one. The variable $\phi_{sep}$ is the separation in azimuthal angle between centres of the sectors