I have tried again the simple and obvious ‘Pressure Driven Analysis’ setup (this sim run is still there), with Inlet face set to 961Pa and the Outlet face set to Mean pressure of 0 Pa and the sim run looked to be converging (albeit at much higher residuals than I like) but the Area averages on the plenum Faces is just not right and it eventually diverged on all faces (including the Inlet and Outlet faces)
I am using ‘New Mesh Preview’ for my meshes but maybe I will go back to Hex Parametric and see if that helps…