  We investigate the scope of a previous result concerning the behaviour of
fermions hitting a general wall caused by a first-order phase transition. The
wall profile function was considered to be analytic in the real axis. The
previous result is valid for analytic functions in the whole complex plane
except in certain isolated singularities located out of the real axis. A
non-analytic profile function in the real axis is studied in order to show the
validity of the result for any profile which can be put as a certain limit of a
function which verifies the latter. A new understanding of the high energy
behaviour of the quantum reflection caused by a sharp profile, as the step,
arises from that study.
