The results are organized in four subsections. First, we introduce HEPTA-INVEST15, a new benchmark set of 15 mono-substituted heptazine molecules with EOM-CCSD-computed ∆E ST values. Second, we analyze intramolecular CT correlations with ∆E ST and test gener-alization to multi-substituted systems. Third, we assess correlations between Hammett parameters and excitation energies. Fourth, we examine how deviation from single-excitation character relates to the inverted energy gap.