Whether the silver complexes are adsorbed in the emulsion or trapped in the the paper fibers is really immaterial in a practical sense. What is important is the kinetics of the process. The silver complexes in film and RC papers are removed much more quickly with washing than those in FB papers. So what controls the rate of silver removal in FB papers is absorption on the paper base. In any set of kinetic reactions it is the slowest reaction which determines the overall speed.