Extract Reflection coefficient from E-field distribution

I illuminate a structure with a Gaussian beam in HFSS. (Gaussian beam wave)
Now, I want to calculate the reflection coefficient.
Therefore, I define a big surface and I calculate the power flowing through that surface. (integration of time averaged poynting vector)
In this way, I compute both incident and scattered power from the structure.
Now, in order to calculate reflection coefficient I take the square root of the power ratio (scattered/incident).
Is that the right way to calculate the reflection coefficient?

Thank you.

Hmmm,

I like the idea. I would be inclined to use a plane wave to illuminate the model. I would also sice the big surface to match the swept surface of the target. You might do a bit of poking around in the radar cross section literature to see what they do,

Regards,

Azulykit

Well, there is a reason I have to use the Gaussian beam approach (focus energy in the structure)
At the same time HFSS (the software I'm using for the simulations) does not support RCS calculations for Gaussian beam illumination.