The kinetic energy of recoiling nucleus were weird

The recoiling energy was calculated using Geant4 when 24keV neutron bombing Argon nuclei and Xenon nuclei, the results were weird, for Argon nuclei, the result was consistent with theory, here is result from

the theory value is:

the results are totally consistent.

but when changing Argon nuclei to Xenon nuclei, the result from Geant4 is:

but the theory value is:

the max recoiling energy is 1.05keV, it is greater than the theory value 0.76keV.
where does the extra energy from the recoiling Xenon nuclei come from?

_Geant4 Version:_11.01
_Operating System:_Ubuntu 20.04
_Compiler/Version:_GCC 9.4.0
_CMake Version:_3.16