  Recently, the electronic analogy of the anomalous spatial shift, including
Goos-H\"{a}nchen and Imbert-Fedorov effects, has been attracting widespread
interest. The current research on the anomalous spatial shift in interface
electronic reflection is based on the paradigm of linear approximation, under
which the center position of the incident and reflected beams are obtained by
expanding the phases of relevant basis states and scattering amplitudes to the
first order of incident momentum. However, in a class of normal cases, the
linear approximation can lead to a divergent spatial shift in reflection for
certain incident angles even though the corresponding reflection possibility is
finite. In this work, we show that such non-physical results are caused by an
abrupt change in the number of the propagating states at critical parameters,
and can be resolved by calculating the center positions of the scattering beams
beyond the linear approximation. Moreover, we find that the beam width has an
important influence on the spatial shift near the critical angles. We
demonstrate our idea via concrete calculations of Goos-H\"{a}nchen and
Imbert-Fedorov shift on two representative models. These results are beneficial
for clarifying the scope of application of the linear approximation in the
study of anomalous spatial shifts.
