Post-pixelized Gaussian profile fits (orange) to prominent emission-line groups (black) in the NIRSpec IFS spectra of the PN SMP LMC 58. The IFS mode G140 disperser is illustrated here as an example among the nine combinations analyzed in this letter. The top row corresponds to the G140M/F100LP configuration (i.e., medium resolution), and the bottom row to G140H/F100LP (i.e., high resolution). The principal line within each group is annotated in the corresponding panel. The individual line wavelengths fitted in each group are marked with dashed blue lines. All of these lines are fitted simultaneously to directly constrain the parameters in σ_inst′(λ) from Eq. (2).