Boost factor K_B vs. energy for the fits presented in Fig. 13. Solid lines denote K_B(E) for different values of K_V: black – K_V = 1, green – 0.6, blue – 0.4, cyan – 0.3, magenta – 0.2. Dashed vertical lines denote the energy corresponding to τ = 1: black for the G12 EBL model, red – KD10, green – F08, blue – KD10 as implemented in the ELMAG code. Solid vertical lines denote the energy corresponding to τ = 2 (the same meaning of colours as for dashed vertical lines).