Regardless of the chosen method for optimizing the CI problem, the orbital representation is also very important. In the particular case of the benzene stack, choosing fragment-localized orbitals enhances the locality of electron correlation within each fragment, and the sparsity of the many-body eigenvectors. Truncations (via GAS, NOCI or ASD-DMRG) that take advantage of the sparse structure of the wave functions have negligible impact on the accurate description of correlation effects and on the predicted total and relative energies.