  We investigate the staircase model, introduced by Aliosha Zamolodchikov
through an analytic continuation of the sinh-Gordon S-matrix to describe
interpolating flows between minimal models of conformal field theory in two
dimensions. Applying the form factor expansion and the c-theorem, we show that
the resulting c-function has the same physical content as that found by
Zamolodchikov from the thermodynamic Bethe Ansatz. This turns out to be a
consequence of a nontrivial underlying mechanism, which leads to an interesting
localisation pattern for the spectral integrals giving the multi-particle
contributions. We demonstrate several aspects of this form factor
relocalisation, which suggests a novel approach to the construction of form
factors and spectral sums in integrable renormalisation group flows with
non-diagonal scattering.
