Firing Order

I was just in a battle with the French and with their nation specific SA "Exellent Spotting" you have to fire the French in the most advantageous way possible to get the most out of the ships. Is there a reason I wouldn't be able to fire the secondaries of the Strasburg then fire the mains of the Richelieu at the target. Them fire the secondaries of the Richelieu to trigger the mains of the Strasburg? The big debate we had in our battle was that each ship had to finish its fire before moving on to the next. In my mind, this makes the "Excellent Spotting" SA, and the French since this is their big SA,less valuable. How do you guys play it?

Thanks,
Brent