The carburetor for the AF engines did have a smaller orifice venturi (and smaller jet orifices as well).
Here is an original, April 1931, document from Zenith, France indicating the size of the AF single venturi. See the blue arrow indicating that the venturi of the carburetor for the AF engine is "18" compared to the venturi for an A and AA engine is "21.5" (look under the "Diff" column):
"Diff" =
Diffuseur, the french word for venturi
So based on the measurements that you show of your mystery venturi, it seems like it is not a venturi for a Model AF engine.
Brad in Maryland