How to set up the port?

Dear all,

I use RF module constructing 2 models, which have same structures except the length. The input power and other parameters are also the same. But after simulation, the power at the incident port of both models are not equal. I want them to have a same value in order to compare the wave and study the dissipate power along distance. I already use a scattering BC. The characteristic are similar but still not equal. So, I wonder that is there any way to set up the structure to have a same input power after the simulation?

Thank you in advance