Time-integrated phase space histogram of particles over particle position x and pitch-angle cosine μ in HTF for the simulation box extending to 20 d_i upstream and downstream for the λ_trans mean free path profile (first from left), minimum mean free path factor of 10⁻⁴ (second from left), minimum mean free path factor of 10⁻⁵ (third from left), and minimum mean free path factor of 10⁻⁶ (fourth from left).