You have highlighted an interesting conundrum ! Certainly I would agree the peloton (or platoon) was the basic drill unit (as it or section is in the modern army). After 1809 it was rare for the French to form composite elite battalions.
Unfortunately I have not been able to track down a copy of
the 1814 "Evolutions Par Brigades Ou Instruction Servant De Développement Aux Manoeuvres De Ligne, Indiquées Dans Les Règlements ... Destine Principalement Aux Officiers Infanterie"
[ Meunier, Hugues-Alexandre-Joseph (Général Bon). Évolutions par brigades, ou Instruction servant de développement aux manoeuvres de ligne, indiquées par les réglements, par le baron Meunier,... Paris: Magimel, 1814. vi, 79 p., 16 pl.; 8vo. - I understand there is a microfilm copy located in the Archives in the First Corps of Cadets but cannot access.]
or the 1809 "Instruction Concernant Les Manoeuveres De L'Infantrie Donne Par L'Inspecteur General De L'Infanterie De L'Armee Du Rhin" - now found at http://126.96.36.199/babelfish/trans..._sect_id%3D105 but it relates to 1791
or the 1813 "Manual D'Infanterie Or Resume De Tous Les Reglements, Decrets, Usages, Et Rensignements Propres Aux Sous-Officiers De Cette Armee"
which would I think give us the whole answer.
But according to Colonel H C B Rogers "Napoleon's Army" page 70 "…battalion columns could be either by division (double companies) or by platoons (single companies)."
General Renard's 1857 book on "Infantry Tactics" shows French 6 company battalions with 4 company squares - this link should take you to the correct page
Looking at Bukhari "French Napoleonic Line Infantry" page 9 - he shows a regimental square with the fusilier companies in 4 company squares and voltigeurs & grenadiers linking them. So clearly there must have been a set of manouevres to enable them to get to the required square formation.