Variation in FIR-estimated parameters along model filaments in cases of: isotropic illumination (frames a–d); a 590 L_⊙ point source at Δy = 2.09 pc and 0.93 pc behind the filament (frames e–h); and to one side of the filament (frames i–l). The plotted quantities are the ratio between the estimated and true FIR optical depths (τ/τ₀), the Plummer parameters (R and p), and the filament FWHM calculated based on these. Each frame shows results for three model filaments with peak column densities N(H₂) = 10²² cm⁻² (blue lines), N(H₂) = 3 × 10⁻²² cm⁻² (cyan lines), and N(H₂) = 10²³ cm⁻² (red lines). The dashed lines in frames a–d correspond to cases with a higher isotropic radiation field (χ = 10); all other cases include an isotropic field with χ = 1. True values are plotted with dashed black lines.