The relation between the commandant supérieur, général de brigade Buquet, and the commandant d'armes, major Saint-Loup, was fixed by an Imperial decree of 24 December 1811, which regulated the organisation and duties of the staffs of the fortresses (art. 26, see also art. 2 & 3):

http://books.google.de/books?id=-N4xAQAAMAAJ&pg=PA93&dq=26

Still mysterious, how Buquet and Saint-Loup could be merged in one in the perception of the Allies.