Comparison between our approach and 3D-PDR simulations. The x-axis denotes the input CRIR of each simulation, where the CRIR in each simulation is treated as uniform. The y-axis denotes the ratio between the calculated CRIR and the input one $\left(\widetilde{{\zeta }_2}/{\zeta }_2\right)$ at A_v = 20 mag. The black horizontal line represents the fiducial value and the horizontal dotted lines represent 50% of the deviation from the input values. Orange, green, and blue dashed lines represent results at n_H = 10⁴, 10⁵, and 10⁶ cm⁻³. The external FUV intensity for all simulations is normalized to the Draine unit (χ/χ₀ = 1).