I'm not sure that is correct,.
Officer-Losses of the Napoleonic Wars (French and French Allies)
has Spain causing only about 25% of officer casulties, about the same as Russia 1812, and the 1813 campiagn.
Napoleonic Wars casualties - Wikipedia
is much teh same.
The problem is in the sources.... in officer-losses Losses of Life in Modern Wars: Austria-Hungary; France Oxford : Clarendon Press; 1916. you can read in archives.org... Gaston Brodart is....very naive ... it is not based on every action, but on samplings of great battles (in a work that deals with since the Middle Ages) and I guees in Martinien´s tableaux....by other side Brodart is writing about each war from Medieval times!!!
About wikipedia I can see no Contemporanean sources...
Who wrote Napoleon suffered 46% casualties in Spain (Portugal too, of course) are French Sources...and that it ´s has been attached to the collective mind...
According with French sources, the Imperial Army between 1804 to 1815 sustained around 900.000 dead.. between them, 32% were KIA (Killed in Action) and DOW (Death of wounds).... out of that 32% that they died in action or because of action (as the dead by wounds)... the 46% were substained in what is named the " funeste guerre d'Espagne (The deadly Peninsular War).
The other 68% dead were accidental dead but most of them... because of Illness: as typhus (la plus terrible de toutes les maladie = The worst disease)... followed by septicemia, malaria, pneumonia, intestinal diseases
And with regard the French Soldiers (from France) not the Empire (German, Italian, Dutch etc etc)... Les perters militaires sont dues pour plus de la moitié à la guerre d'Espagne. (about French military casualties more than half were sustained in the Peninsular War)
Cette malheureuse guerre d'Espagne m`a perdu. (Napoleon Ièr)
Bourgeois-Pichat, Jean: Evolution générale de la population française depuis le XVIIIe siècle . 1951
Houdaille, Jacques: Le problème des pertes de guerre, Revue d'Histoire moderne et contemporaine, 1970 (about casulties in general, in French language. Interesting)
Meynier, Albert: Levées et pertes d'hommes sous le Consulat et l'Empire, Revue des Etudes napoléoniennes, 1930,