Please point out where I said you know the blast radius and which direction it heads. Not to mention it's an analogy and I'm not a bombing expert. You can probably figure out my point.
That would be an impossibility with WWII technology. It's irrelevant -- the scenario you described already acknowledged the bomb crossing the border and killing French citizens on the other side.
"On an Italian border." Where else could the blast possibly go, except on both sides of the border?