I say again!
This dilute fixer must maintain the silver complex solubility during the early stages of washing. I have actually seen dilute fixers work, only to fail when washing starts. Silver halide complexes re-precipitate out into the coating as the wash water begins further dilution and the complexes become insoluable again. They end up in the film or paper. Usually, film is most susceptable, but Baryta FB papers have been known to do this in the Fibre Base.
Sorry, but this is a fact. As many as 4 or more complexes form depending on fixer concentration and they all vary in soluability during the wash. One must be very careful.
You are making a broad statement that is not always true!