Estimated p and R values and the corresponding FWHM as a function of the peak column density of isotropically illuminated model filaments. The black, blue, and red curves correspond, respectively, to observations of model filaments in a normal ISRF, χ = 1, and in stronger fields with χ =10 and χ = 100. The solid lines with circles are fits to the model profile at |r| < 0.58 pc, while the dashed lines with squares are fits to a narrower region, |r| < 0.35 pc. The horizontal dotted lines indicate the true parameter values in the models.