We present a joint experimental and theoretical investigation to resolve the discrepancy in the ratio of relative peak cross sections for narrow atomic resonances among various experimental spectra and also between theory and experiment. Our study includes an effort to measure both the absorption and ionization spectra in a single experimental setup. We also present a careful analysis of the effect on the resonance structure due to the Doppler broadening at finite temperature when the Doppler width is greater than the natural linewidth of the resonance. In addition, we demonstrate that the column density strongly affects not only the absorption structure profile of a narrow atomic resonance but also the ionization spectra measured in an ionization chamber. From the good agreement reported in this article between the observed and the theoretically simulated spectra for the pressure-dependent peak cross sections and the effective asymmetry parameter for the lowest resonance of the He (1,0)(2)(-) series, we are able to characterize the monochromator (i.e., slit) function of a given light source, including its estimated energy resolution.