To add a little:
Just remember that all of the MkI, MkIII series sights were originally issued with the small apertures.
IIRC it was a post-war Britishproject to ream the sights "battle apperture", most (all post-war?) of the Fazakerly ones will have been produced with large apertures (actually I somewhere have a copy of the post-war Canadian instruction where it says that all new sights will be so reamed, but old ones are to be left alone).