Ok slightly modified setup with coax
Setup:
Signal generator into coax then some alligator clips 0.01uF cap at tp17
ch2 set probe at 10x at cap/tp17
ch1 set probe at 10x at tp20
Scope set to 1x for both channels
Signal generator set to 400mv at 11.996MHZ? (voltage input less here since clearly coax caused less loading and more output voltage)
Measurements:
CH2 measured 9mv p-p * 10 = 90mv
CH1 measured 7mv p-p * 10 = 70mv - saw ~2khz output tone
Estimated ~-2db loss