Please comment on this OptiSurface4D bounded by ridges. Does it effectively force everything away from the edges and into the meandering middle?
Yes but be careful that the subzones are wider than 1.5 x calculation grid spacing so all grid points along the boundary are working to block the flow. Your subzones are too thin here.
Ridge Subzones act like barriers to water flow so if you put one on the edge of a field and the water naturally flow out there, OptiSurface will try to adjust the topography so that water can leave the field somewhere else.