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The prediction of multiplet energies of dn ions such as transition metal ions in crystals is important for the development of novel optical materials. The first-principles calculations of the multiplet energies can be performed by the discrete variational multi-electron (DVME) method which is based on the configuration-interaction (CI) approach. Although the mutiplet energies calculated by CI calculations are generally overestimated, the overestimation can be corrected by considering the configuration-dependent correction (CDC) and the correlation correction (CC). For example, the experimental multiplet energies of V3+ and Cr3+ in α-Al2O3 were well reproduced by first-principles calculations considering CDC-CC. However, for d5 and d6 ions, the conditions of CDC-CC such as the considered transition processes have not been established. In this study, in order to optimize the conditions of CDC-CC, we performed first-principles calculations of the multiplet energies of Fe3+ and Co3+ in α-Al2O3 considering CDC-CC based on various transition processes. As a result, we could optimize the conditions of CDC-CC for Fe3+ and Co3+ in α-Al2O3 and successfully reproduced the experimental multiplet energies. By consideration of CDC-CC, the repulsion between electrons was suppressed and the overestimation of the multiplet splittings was reduced.