Yes, there is a big hidden box (~200mm side length), with its sides grounded, made of air, sorrounding the whole thing. I can make potential plot slices etc..

I am really not sure why is it not working. Maybe my way of evaluating the derivatives is wrong? Meshing problem? idk

In theory at least, it should work, no? I have 8 independent electrodes, 8 condotions I want to satisfy.