Reversal level of the Mg II h line (first and third columns) and k line (second and fourth columns) against physical parameters for the isothermal isobaric models (first two columns) and the PCTR models with γ = 2 (last two columns). Top: reversal level vs. central temperature, colour scale indicates pressure. Middle: reversal level vs. central pressure, colour scale indicates temperature. Bottom: reversal level vs. slab thickness (for isothermal isobaric models) or column mass (for PCTR models), colour scale indicates temperature.