Top: modeling of I + V (red curve) and I − V (green curve) for Fe i 6301.5 Å  in the presence of a magnetic field and velocity gradient (here η₀ = 0.8, ξ = 50, B = 1000 G, ψ = 60^o, and δv = −800 m s^-1. The blue curve is for the I Stokes. The plotted stars define the bisector positions derived at different depths in the profiles, and the black stars represent the bisector half summation. P_c is the intersection point between I + V and I − V that is distinct from the I Stokes minimum. Bottom: modeling of the corresponding V Stokes. P_z is the position of the Stokes V zerocrossing.