  The study of low-yield effects requires not only good quality of the original
data but also puts high requirements for their processing procedures to
increase the efficiency of the selection of useful events. The exploiting of
the large cylindrical proportional counter's electrostatic topology allows
improving the extrapolation of information about the primary ionization of a
multipoint event. Long-term calibration measurements with an external
$^{109}$Cd-source allowed the development of a new method for analyzing the
pulse shape from a sizeable proportional counter. Optimized analysis of the
current's pulse shape from the electron cloud of primary ionization in the
counter improved the resolution and energy calibration. As a result, the
efficiency of selecting useful events was increased by 25\%.
