nice work, i read that the C meter will read the impedance of the wfc, not specifically the C, JLN shows a difference between his calculated and measured too, and he actually found resonance, apparently, maybe his results would be worth another read for you at this stage in the game, maybe get some more ideas.
Also, I'd be interested to see if you can reproduce mine and warps results on your delrin cell, because I found lots of em interference being thrown off the cell, the delrin is probably supposed to direct all that energy into the water gap.