Radial velocity for selected wind models. The black line denotes the model without either X-ray irradiation or clumping, while blue, red, and green lines denote models with the same X-ray irradiation (with the same L_X and D) but with different clumping: without clumping (blue, solid), with C_c = 3 (red dotted), and with radially dependent clumping factor after Eq. (6) with C₁ = 10 (green dashed). Arrows denote the location of the kink in the velocity profile with a corresponding value of the ionization parameter from Eq. (12). Upper left: model 300-1 with L_X = 10³⁷ erg s⁻¹ and D = 300 R_⊙. Upper right: model 375-1 with L_X = 10³⁷ erg s⁻¹ and D = 100 R_⊙. Lower left: model 300-5 with L_X = 10³⁵ erg s⁻¹ and D = 30 R_⊙. Lower right: model 375-5 with L_X = 10³⁶ erg s⁻¹ and D = 100 R_⊙.