The actual organization of French forces during the 1813 Campaign in Germany is not easy to be simulated.
In the early phases of the Campaign, Napoleon disbanded the Army of the Elbe: Corps were merged in the Army of the Mein, (later Army of Germany), Eugene was transferred to assume command of Army of Italy.
During the Campaign Napoleon was in command of the full Army of Germany, although in different moments Corps were detached to form independent Commands: Army of the Bober, Army of Berlin, Murat command at Leipzig. These Army level Commands assigned in turn to McDonald, Ney, Murat were anyway subordinated to Napoleon's control and supervision.
The Emperor, while having direct control over a sort of mobile Grand Reserve, (including The Guard, and other ad-hoc Corps) operated as a modern Group of Army commander, directing and supervisioning moves of all Marshals' armies....At least he tried, with the limits of the communication and control system of the age.
All that cannot be simulated in NCP, being Army the only superior command level.
So, French stacks of more Corps operate away from Napoleon's HQ, they miss the support of an own Army HQ and cannot resot to coordinated movement ability.
My suggestion is to add to French OOB, possibly included into Napoleon's HQ Force, one ot two unattached HQ units: player could be use them to create ad-hoc indipendet Army level commands during the campaign.
When created, these Army-Commands will have all advantages of an NCP army: Corps coordinated movement, own Army HQ support. As a drowback, Corps of any new army will loose benefit from beeing under Napoleon direct command, (see Napoleon's superior ratings).
JastaV