Changing slope of the optically thick pressure levels (p_gas(τ(λ) = 1) within optical to mid-IR wavelengths (0.2−30 μm). The dashed blue line indicates the location of the sodium line, and the coloured bars show the wavelength ranges of various missions. Top left: τ(λ) = 1 slopes for the morning and evening terminator, the substellar point (ϕ = 0°, red), and the antistellar point (ϕ = 180°, dark blue). The remaining plots show parameter studies for the evening terminator (ϕ = 90°, θ = 0°). Top right: different mixing efficiencies. Bottom left: effect of cloud particle porosity. Bottom right: effect of element abundances.