Adapt the principles of Impetus to the Napoleonic - or any other - era. 'Grandeur' provisional rules can be a guide. A block of troops is assigned a combat value relative to their historical allies and opponents. French cuirassiers might be 6 in the Waterloo campaign, Dutch-Belgian hussars might be 3, relatively speaking while the ill-famed Cumberland hussars might only be 2. You can organise these blocks depending on scale of figure and scale of game. In 40mm Nap., my 'regts' consist of 6 bases, each a company of 12 figures. In 12mm WSS, each base represents about 200 men and contains about 48 figures. In my homage to the 15mm North African campaign of early 1942, a typical squad of 10 men fits with sufficient space of a 120mm x 60mm base o look like it might have been. Whether I call these units squads, platoons, companies or btns/regiments doesn't really matter. They have a particular combat ratio to each other.
We ask a lot of rules writers, I think, to roll out clauses for every concievable tabletop eventuality. Just adapt the set that grabs you most and pay respect to this fine body of rele-writing men,