I was having trouble believing that the new cell (no.10)wasn't out performing no.9, especially since it is on the heater.  As I fidgeted with it, adding some more insulation and playing with the wires I noticed something.  The output was steadily dropping the more the cell was jarred, the cathode was sinking!  Well, actually the cathode was sinking but the substrate was also rising a bit due to microbe activity.  So I tightened up the guy wires holding it in place and WOW!

10:32am Oct 4,2019 it peaked at about 405mv and is slowly coming down, we'll see where it lands.

Here you can see the cathode being held up so it is barely making contact with the substrate.

I think with the next cell I will mount the copper mesh completely above the substrate with a spike or brush that connects it electrically.  This will maximize the O2 surface area and should allow the anode-cathode "substrate" distance to be tuned easier.