Discrepancy in cross-section for electron-positron annihilation and muon-anti-muon annihilation

I am trying to compare the cross-section for various electron-positron annihilation to that of muon-antimuon annihilation. For this, I am using the model sm-lepton_masses which also takes into account of the lepton masses in the reaction.

I have performed various processes like:
e+ e- > a a and mu+ mu- > a a for cmenergy = 200 GeV, 300 GeV, ...., 2 TeV
e+ e- > z a and mu+ mu- > z a for cmenergy = 200 GeV, 300 GeV, ...., 2 TeV
e+ e- > h a and mu+ mu- > h a for cmenergy = 200 GeV, 300 GeV, ...., 2 TeV
and so on. I am giving the script I am using here:

import model sm-lepton_masses
generate mu+ mu- > a a
output mutoaa
launch mutoaa
set ebeam 100
launch mutoaa
set ebeam 150
launch mutoaa
set ebeam 200
launch mutoaa
set ebeam 250
launch mutoaa
set ebeam 300
launch mutoaa
set ebeam 350
launch mutoaa
set ebeam 400
launch mutoaa
set ebeam 450
launch mutoaa
set ebeam 500
launch mutoaa -i
print_results --path=./cross_section_mutoaa.txt --format=short

This one is for the first process. Similarly just by changing the particles and the products, I can get the values of the cross sections for other processes as well. The problem is, all the cross-sections for both the electron-positron annihilation and muon-antimuon annihilation comes out to be exactly same for all the processes no matter what process I am trying to compare. Muon is approximately 207 times heavier than the electron. I understand that the mass difference is not huge in comparison to the centre of mass energy, but in my point view, it is significant enough to have an impact on the cross-section. How can it come out to be exactly same?

If anyone could help me in this regard, I will be really grateful.