Input Z is 200 Ohms. The 11.5 dB loss is a power loss. The voltage loss is 5.5 dB (basically the voltage divider between the 200 Ohm input Z and the 174 series R).
If you turn the L-pad around and have a low impedance source driving it and then terminate with 50 Ohms (like how the output of the AD8367 eval board is done), the voltage loss is 17.5 dB. But the power loss is still 11.5 dB.
Does that make sense? I can attach some math if need be.
Joel