ImplicitPrefactor 1/(2Pi)^D

[sunnyasquabla]

Hi I am evaluating the amplitude for the decay process Higgs to gamma gamma.
For that I generated diagrams using FeynArts (diagrams with loops via W loop, top loop and scalar loop).
And then I evaluated the amplitude using FeynCalc. I am getting a correct result for W loop and fermionic loop.
For scalar loop I had to define a new .mod file for which I used FeynRules.

While evaluating the scalar integrals using FeynHelpers I had introduced a prefactor of 1/(2Pi)^D in case of W loop as well as top loop as mentioned in the manual.
But for scalar loop If i introduce the same prefactor then I am getting a wrong result. The results matches only after I remove the extra prefactor of 1/(2Pi)^D for the case of scalar loop.

I want to know why is that?

Thanks in advance.
Si