Inductor gets me puzzling in my Microstrip Amplifer design!!

Hi, I' designed a distributed amplifier using ADS for Agilent GaAs FET transistor with some specific S-parameters for a gain equales 13dB.When I did the simulation everything was alright and as I planned.But I add a(just from my self) extra thing to my design which is an inductor in the output stage then suddenly the gain increased to 17db(I add this value by trial and error method).My question is what the shunt inductor did to my amplifier in the real?.Realy I couldn't
justify putting the inductor to increase the gain while my inductor reactance at my central frequency is 0.08 ohm which means this is a grounding wire.
My amplifier consists of foure microstrip lines two in the input and the others in the output for matching purpose.The additional inductor is lumped elements

Doesn?t matter if the reactance of the inductor is low, if in this way the circuit provides the best output match for the highest gain.
The isolation of the amplifier (S12) plays an important role getting the proper gain when changing the output match.