  We discuss chiral perturbation theory for two and three quark flavors in the
epsilon expansion at next-to-next-to-leading order (NNLO) including a small
imaginary chemical potential. We calculate finite-volume corrections to the
low-energy constants $\Sigma$ and $F$ and determine the non-universal
modifications of the theory, i.e., modifications that cannot be mapped to
random matrix theory (RMT). In the special case of two quark flavors in an
asymmetric box we discuss how to minimize the finite-volume corrections and
non-universal modifications by an optimal choice of the lattice geometry.
Furthermore we provide a detailed calculation of a special version of the
massless sunset diagram at finite volume.
