  We develop a new way to calculate the overlap of a boundary state with a
finite volume bulk state in the truncated conformal space approach. We check
this method in the thermally perturbed Ising model analytically, while in the
scaling Lee-Yang model numerically by comparing our results to excited state
g-functions, which we obtained by the analytical continuation method. We also
give a simple argument for the structure of the asymptotic overlap between the
finite volume boundary state and a periodic multiparticle state, which includes
the ratio of Gaudin type determinants.
