"As the the "divisions" - in case I understand the quote correctly - it means Divisons in the sense of corps divisions and not of divisions of two companies."
I agree that it doesnt mean divisions as in two compagnies, but as in two lignes.
I also agree that the Colonne Vuide was not to deploy en tiroir but en eventail. It is for that reason the flanking battalions were en colonne d'attague or colonne par division serree (a colonne par divison serree can operate just like a colonne d'attaque).
What we need to find is the General Instructions for Italy. So I shall continue going through any Revue Militaire a l'Etat-Major de l'Armee that may pertain to Italy. And I shall also assit in digging through Pelet. I do not recall Ney mentioning a Colonne Vuide. Nevertheless I will also look through Ney on the off chance.
Of course this portion of MacDonalds of the event that he wrote, sounds like two line deployed:
"...je faisais serrer au sur et a mesure que des files etaient hors de combat, et tirer les alignements comme a l'exercice. sur ces entrefaites, voyant la cavalerie s'ebranler pour me charger, je n'eus que le temps de faire serrer la seconde ligne sur la premiere; les deux divisions encore en colonne les flanquerent, et ce carre fut ferme par une portion de cavalerie de la division du General Nansouty."
Of course we could ask Jake Gill, he wrote a book on the matter, but I do not want him to give up anything he wouldn't want to share because of his book that is still on the market.