Evaluation of the vertical eddy diffusivity DZ

I see that Dz is computed using the Reynold’s analogy, where Dz is related to the vertical eddy viscosity Az according to Dz=0.14Az This corresponds to considering a turbulent Prandtl number equal to Pr=Az/Dz=1/0.14~7, which is the molecular Pr of water. I was expecting a Pr~1, which is the turbulent Pr for water. Why the factor 0.14 is used instead? Thank you