To better understand and provide rationale for the CVS-uS resolvent as an approximation to the fc-CVS-EOM-EE-CCSD resolvent for computing X2PA moments, Tables and present the configurational channel analysis of the 2PA moments between an initial (EOM-EE-)CCSD state with frozen core and a final fc-CVS-EOM-EE-CCSD wave function. We define these 2PA configurational channels as the 2PA coupling terms between Slater determinants involved in the wave functions of the initial and final states through the Slater determinants involved in the intermediate wave function. Here, we neglect dynamical correlation effects arising from the cluster operator T . Our aim is to understand which 2PA channels are fully captured, approximated, or not captured by the CVS-uS approximation to the fc-CVS-EOM-EE-CCSD resolvent. In addition, the channel analysis can help us better understand the impact of different types of bound and continuum intermediate states on the 2PA moments. First, we consider only the dominant electronic configuration in the initial wave function, such that Ψ g ∼ Φ 0 for the CCSD state and Ψ f ∼ Φ b J for the core-excited final state. Within this simplified model, there are just four 2PA channels that need to be considered-the first two channels in parts (i) and (ii) each of Tables and. The two channels in part (i) are captured exactly by the CVS-0 resolvent, relative to the fc-CVS-EOM-EE-CCSD resolvent, and dominate the contributions of coreexcited states that typically lie below the coreionization potential. These channels can also show resonance enhancement when one of the two absorbed photons is in the infrared/UV-vis regime and the other is an X-ray photon that is nearly resonant with a core-excited state. Similarly, the two channels in part (ii), which are only approximated by the uS resolvent, relative to the fc-CVS-EOM-EE-CCSD resolvent, can show resonance enhancement when the infrared/UV-vis photon is nearly resonant with a valence-excited state.