Have you tried using a chemical foggant rather than re-exposure to light? While it is hard to have too much re-exposure it is possible. A simple 2nd developer using sodium sulfide will act as a fogging developer. You might get better results with chemical fogging.
I would think I would still get fog using a chemical foggant vs exposing to light. Developer can only develop the active silver that remains. It's my observation that it should not have existed.
Is it possible for the second developer to leave behind a fog, even if there is no silver present?