[Ifeffit] limits for second shell

Hi, I have a sample of a pure Er2O3 (blue line in the attached graph) and a sample of doped ZnO with erbium that has segregated the same oxide (red line) by thermal treatmen. The signal for de segregated oxide gets noisy around k=9 because the sample is so diluted, but the radial distribution shows second shell signal, smaller than the pre oxide, but still a signal. My doubt is about how to know if the second shell is real and if that second shell can be useful to obtain information. Is there a criteria to know that? Some limit in k-space? Thanks, euG