Active medium in laser cavity

Hi,

I am new to Comsol, and I am working on simulation of laser cavity. When I simulate the active medium, I just set the imaginary component of refractive index to negative in material properties. And then I used ewfd.intWe to plot the total electric energy inside the structure with a range of complex refractive index. The thing is that the energy doesn't go up as I expected, it goes up and then deceases when further decease in imaginary of refractive index. Can anyone help me understand that?