Hi Thomas. I think we have met before on this topic, when you thanked CT for this post. Why are you persisting with the same misinformation?
http://www.talkphotography.co.uk/forums/showthread.php?t=10271&highlight=curtain
The example shown proves that it makes no difference at all
to the relative exposure levels of flash and ambient light whether the flash is fired first or last.
If a better understanding is helpful to others, I will debate anything with anyone, including Joe McNally, when I think what I am saying is right. Slow-sync photography, dragging the shutter if you like, and fill-flash have been favourite techniques of mine for several decades. I think I've tried everything, including second curtain sync, in clubs and parties, and I think I know how it works.
In the situations cited here, first or second curtain sync makes no difference. But to imply that second curtain somehow reduces ghosting of the ambient image, which is what you're suggesting, is not true. If it was, the whole theory of exposure would be turned on its head.