  We show how the leading physical and Wilson low-energy constants associated
with Wilson fermions in lattice gauge theory can be determined individually by
using spectral information of the Wilson Dirac operator with fixed index at
finite volume. The methods are demonstrated in simulations with leading-order
improved Wilson fermions. In addition to the expected suppression of the
leading term in Wilson chiral perturbation theory we observe a substantial
reduction also of the higher-order Wilson low-energy constants.
