Thanks, syzygy and sunray.
Always impressed by the ingenuity of these puzzles.
Thought for a while this one would be unusually easy, but there were some interesting wrinkles.
My grid is complete but I’m feeling dense regarding the two-clue entries. I can see what they have in common but not how they would be arrived at independently.
It took me a(n embarrassingly) long time to see how the four unclued across solutions were derived from the pairs of referenced down solutions. Is that what you're referring to?
Afraid so. When I post something like this I almost invariably see the light within seconds, but I haven’t been dwelling on it. I do make a connection with “tandem with a charge” but that’s probably off-track. I’m prepared to be embarrassed.