Wow, that's an extremely high resistivity. I doubt if your diaphragms can really be fully charged.
If I were you, I would go for a bit thicker spacers, and put on a less resistive coating.
For my Float clone, I couldn't get the right tension and stability when using 0.5 mm spacers. In the end, I cut a piece of 0.1 mm thick plastic sheet as extra spacers. It's amazing to see how the extra 0.1 mm can help stabilize the diaphragms.