Effective Doppler dimming coefficient of the resonantly scattered H I Lyα line (solid lines) and absolute value of its derivative with respect to the outflow speed (dashed lines), calculated at the heliocentric distance r = 2.5 R_⊙, on the plane of the sky of the observer, for a polar coronal hole (CH) with T_HI = 2.2 MK averaged along the LOS (red lines), and r = 4.0 R_⊙ for an equatorial streamer (STR) with T_HI = 1.6 MK averaged along the LOS (green lines).