I built the shroud to avoid air recirculating through the rad and to avoid using the poke through the rad zip tie mounting system the fans came with. Air can't recirculate without going under the front bumper and back through the grill.
When/If I open up the top left and bottom right corners of shroud I'll do some kind of grill / flap to stop recirc when the fans are on.
the fans are very effective in this setup, I'll guess they'd have worked fine just hung from the rad with no shroud.
My rad is angled back at the top so the bottom clears steering box, I would have had to use a very thin or small diameter engine driven fan