very simple!
take spar over frequency
calculate Gav and format in dB
then fit the curve with the function:
A=C0*Freq^.5 + C1*Freq^1 [dB]
You have to find C0 and C1, right? ;-)
Then C0*Freq^.5 is the dissipation due to ohmic losses while C1*Freq is the dissipation due to dielectric losses.
Now You may compare, freq by freq the conductor loss with the DC loss and so, calculate the ratio.
The ratio is the conductor section ratio, finally divide by the conductor perimeter, Youll'get the penetration factor.