Using the "Highlight Organization" and clicking a leader icon, I think highlights their whole command.
Also, in all the series I play, I learned years ago to never keep any leaders in the front lines. Keep them right behind or close by and the higher commanders a bit further back to help with rout & reorder.
You need to keep tight lines, but centering the brigade leaders with their formation, will still give their effects to the units, though I don't think as good as being right with them, it still works well enough. With the French, it should be even more effective because of the good ratings & range. The doctrine works well for me with the CSA in the ACW series and they are similar in superior ratings, in most games, like the French are here. Also the Coalition holds up well, even with less describable ratings, ranges & unit quality et al. The only time I might stray from the concept is in cav charges, as a leader can have a good bonus. But I am a bit cautious to charge, given the mixed ratings etc for Coalition cav in most games.
DC's, CC's, Wing Co's etc, are further back in a tiered system so that they provide the check, but can also pick up routed units as they run back. Not the easiest task sometimes as a Coalition player, but I'll usually try to retreat units of the same organization to a central leader and crowd around them.
The whole system has led me to generally lose very little or no commanders in most of my games. The only real badge of honor I can claim for my otherwise terrible game play....
Only some of the extremely best players have been able to pick off leaders and very, very few guys can get at the top commanders and usually because I created a gap in the lines in my ZOC control by accident. As a Coalition player, your higher commanders are often your lifeline and sometimes the only way to keep any sense of order. When they go, the whole thing can go to pot easily.