At the Sirius synchrotron facility, large area photon counting detector systems are employed in different beamlines and experimental techniques. These detectors were developed at the Brazilian Synchrotron Light Laboratory (LNLS), the called PIMEGA series detectors feature Medipix3RX Application Specific Integrated Circuit (ASIC), with 256 x 256 squared pixels and 55 µm pitch. In this work, the influence of the threshold energy level was evaluated in order to achieve optimized values for minimizing false counts during operation, which arise from the charge sharing effect. As a result, we have defined the Approximated Mean Multiplicity (AMM), which can be used as a new procedure in photon counting detectors to define an optimal operation threshold level. Additionally, energy calibrations and energy resolution experiments are presented, as well as the AMM values for multiple operation bias voltages and incident energies.