Need a help in understanding Bode plotter reading??

I made some experiments on L-network Z matching, first I try the circuit without any match (R1 is source impedance and R2 is the load impedance), and got the following result:


Notice: the voltage gain = -0.828 dB @ 100MHz
I repeated the experiment again, but this time using the wattmeter and got:


What I was able to understand from the aove is as follows:
dB power gain = 0.5 dB voltage gain
Our pode plotter gave us that the dB voltage gain = -0.828,
so the dB powe gain = -0.414, and that’s mean P_load/P_source = 0.909
So 90.9% of the source power transferred to the Load.

Now I'll introduce the L-impedance match (Which was calculated by someone)


Notice: the voltage gain = +3.979 dB @ 100MHz
I repeated the experiment again, but as before using the wattmeter and got:


dB power gain = 0.5 dB voltage gain
Our pode plotter gave us that the dB voltage gain = +3.979,
so the dB powe gain = +1.99, and that’s mean P_load/P_source = 1.58
So 158% of the source power transferred to the Load and this is imposible.
The wattmeters show 50% was transfred.
Where the error in my concepts?
Thank you.