  It is believed that the semi-Poisson function $P(S)=4S\exp(-2S)$ describes
the normalized distribution of the nearest level-spacings $S$ for critical
energy levels at the Anderson metal-insulator transition from quantum chaos to
integrability, after an average over four obvious boundary conditions (BC) is
taken (Braun {\it et} {\it al} \cite{1}). In order to check whether the
semi-Poisson is the correct universal distribution at criticality we
numerically compute it by integrating over all possible boundary conditions. We
find that although $P(S)$ describes very well the main part of the obtained
critical distribution small differences exist particularly in the large $S$
tail. The simpler crossover between the integrable ballistic and localized
limits is shown to be universally characterized by a Gaussian-like $P(S)$
distribution instead.
