  In a previous paper [Phys. Rev. A 105, 042205 (2022)], the distribution of
resonance poles in the complex plane of the wavenumber $k$ associated to the
multiple scattering of a quantum particle in a random point field was
numerically discovered. This distribution presented two distinctive structures:
a set of peaks at small $k$ when the wavelength is larger than the
interscatterer distance, and a band almost parallel to the real axis at larger
$k$. In this paper, a theoretical study based on wave transport theory is
proposed to explain the origin of these structures and to predict their
distribution in the complex $k$ plane. First, it is shown that the peaks at
small $k$ can be understood using the effective wave equation for the average
wavefunction over the disorder. Then, that the band at large $k$ can be
described by the Bethe-Salpeter equation for the square modulus of the
wavefunction. This study is supported by careful comparisons with numerical
simulations.
