The FOA-XX Series (FOA-22, FOA-32, etc) are used on the handheld power meters and the reflection from the detector lens will not affect the measurement repeatability.

On the older scientific equipment (IQ-200 power meters, benchtop model, etc), Exfo was using the FOA-2XX series (FOA-222, FOA-232, etc) to minimize the reflection effect and improve the measurement repeatability.

Then the FOA-2xx adapters were improved and replaced with the FOA-3xx (lower reflection from the FOA coating). The design is about the same but the coating surface is different.

The reflection is not from the ferrule on connector but the reflection that occurs from the detector lens to the black surface of the FOA adapter. The 200µm aperture of the FOA-3xx adapter's design will block most of this back-reflection from the lens (or detector) to the ferrule." See diagram in pictures section.