^ ohh ok, I understand what you're doing now. I'll add the ground strap back to the intake tube and see if that reduces my corrections further. If it does, then I know that some corrections were being caused by spurious EMF. That should be an interesting experiment.
Where did you get this mica wafer? It sounds like that would help as well so I'd like to experiment with that too.
I think between our two approaches we should be able to come up with a good solution for these type of intake troubles.