  The analysis of the time profile of electrical signals produced by energy
depositions in germanium detectors allows discrimination of events with
different topologies. This is especially relevant for experiments searching for
the neutrinoless double beta decay of $^{76}$Ge to distinguish the sought-after
signal from other background sources. The standard calibration procedures used
to tune the selection criteria for double-beta decay events use a $^{228}$Th
source, because it provides samples of signal-like events. These samples
exhibit energy spatial distributions with subtle different topologies compared
to neutrinoless double-beta decay events. In this work, we will characterize
these topological differences and, with the support of a $^{56}$Co source,
evaluate biases and precision of calibration techniques which use such event
samples. Our results will be particularly relevant for future experiments in
which a solid estimation of the efficiency is required.
