  Magnetization hysteresis loop $M(H)$ measurements performed on a single
crystalline Ba$_{0.63}$K$_{0.37}$BiO$_3$ superconducting thick film reveal
pronounced sample geometry dependence of the "second magnetization peak" (SMP),
i.e. a maximum in the width of $M(H)$ occurring at the field $H_{\rm SMP}(T)$.
In particular, it is found that the SMP vanishes decreasing the film dimension.
We argue that the observed sample geometry dependence of the SMP cannot be
accounted for by models which assume a vortex pinning enhancement as the origin
of the SMP. Our results can be understood considering the thermomagnetic
instability effect and/or non-uniform current distribution at $H < H_{\rm SMP}$
in large enough samples.
