have you confirmed that the two backplates are isolated from each other?
Are you using a new switch assembly on an old mic?
Are there four wires going to the capsule?
One to a tab on the backplate and the forth connected to the plastic tab holder going through to the backplate.
It seems that one of the backplates wasn't making a connection to the wire tab. There was a small piece of plastic under the tab which I removed and now it's making a connection. My figure 8 is still significantly lower in level.