Left panel: optical depth at the internal shock region as a function of the Lorentz factor of the jet for (L₀, δt)=(10⁵⁰ erg s⁻¹, 0.001 s) and (L₀, δt)=(10⁵¹ erg s⁻¹, 0.01 s), both marked by the black curve, while the blue line corresponds to (L₀, δt)=(10⁵⁰ erg s⁻¹, 0.01 s) and the orange one to (L₀, δt)=(10⁵¹ erg s⁻¹, 0.001 s). Right panel: positions of the jet head (r_h) as a function of the Lorentz factor of the jet for L₀ = 10⁵⁰ erg s⁻¹ and L₀ = 10⁵¹ erg s⁻¹ marked by long-dashed blue and orange lines, respectively. Solid blue and orange lines correspond to the positions of collimation shock (r_cs) for L₀ = 10⁵⁰ erg s⁻¹ and L₀ = 10⁵¹ erg s⁻¹, respectively. The positions of the internal shocks (r_is) for δt = 0.001 s and δt = 0.01 s are indicated with black short-dashed and solid lines, respectively.