Oliver,
I agree that Marshal Davout had chosen convenient numbers to make his considerations simpler. In other armies, the estimation of the frontage per one man was larger than 0.5 meter.

Prussian General Friedrich Christoph von Saldern wrote in 1770s that in open column two divisions of 24 files each should have the interval of 18 paces between them. In an open column, the interval between the sub-units was equal to the frontage of the sub-units. So, he eastimated that 24 files occupied 18 paces. If he meant the Prussian pace of 2 and 1/3 Rhineland feet (0.732 meter), then one file occupied 0.55 meter.

Elemens de la Tactique de l’Infanterie, ou Instructions d’un Lieutenant-Général Prussien, pour les Troupes de son Inspection, no place, 1783, p. 46.
Elements of tacticks, and introduction to military evolutions for the infantry: by a celebrated Prussian General, London, 1787, p. 54.

From the British 1798 infantry drill regulations:

The platoon falls in, in three ranks at close order, with shouldered firelocks; the files lightly touching, but without crouding; each man will then occupy a space of about 22 inches.

Rules and Regulations for the Formations, Field-Exercise, and Movements, of His Majesty’s Forces, London, 1798, p. 33.

22 English inches are rougly equal to 0.56 meter.

Best wishes,
Alexander