The limited number of molecules in the Cheng test set makes the statistical analysis of error less meaningful. Therefore, we have tested the performance of the SS-FNO-IP-EOM-CCSD* method on the test set of Illas and co-workers . R3CVS approximation has been used for the calculations. This test set has been previously used to evaluate the performance of the DLPNO version of the IP-EOM-CCSD method for core orbital . The Illas test set contains a total of 66 molecules containing at least one of the following main group elements: B, C, N, O, and F. A total of 176 core IP values were considered for the analysis for which experimental values are available and the geometries of the molecules has been taken from reference . Table displays the statistical analysis of errors for the SS-FNO-IP-EOM-CCSD*/unc-6-311++g** method, both with and without SFX2C correction, alongside the corresponding IP-EOM-DLPNO-CCSD and SS-FNO-IP-EOM-CCSD results. Figure illustrates the distribution of error in the different natural orbital-based approximations of the IP-EOM-CC method. The calculated IP values in the SS-FNO-IP-EOM-CCSD*/unc-6-311++g** method consistently overestimate experimental results. However, the errors are much smaller than the corresponding CCSD approximation (SS-FNO-IP-EOM-CCSD method) and IP-EOM-DLPNO-CCSD method. It can be seen that the latter method shows a slightly smaller deviation from the experiment than the SS-FNO-IP-EOM-CCSD method in the same basis set. However, the IP-EOM-DLPNO-CCSD method values were calculated using much higher natural orbital threshold of 10 -12 which is presumably the cause for the reduction in the error. However, the inclusion of the triples in the SS-FNO framework leads to much smaller errors, which shows that the error due to missing triples correction is more significant than the natural orbital truncation errors.