Bruce,
Thanks for providing that excellent information. I am amazed to learn that the photo does indeed depict a damper as it appears to. I have never seen such a feature in any other locomotive photo. I was also thinking that if it was a damper, I could not image what the purpose would be.
But the explanation of the function in your patent reference does make perfect sense. It is to reduce the draft that would be drawn into the firebox through the boiler tubes that would naturally result from the steam exhaust through the stack. It would reduce that draft through the firebox by offering an alternative inlet from the front of the smokebox.
I would have been inclined to believe that when working steam, you would always want the full available draft, so there would be no need to reduce it. But apparently this is not the case with a Wootten firebox burning anthracite in a shallow bed across a wide grate. Also, the patent mentions the occasional need to limit the firebox draft after shutting off steam with a hot fire. I guess the point then would be to simply limit the convection draft that would be pulled through the tubes without this damper device.
I see the part you refer to in the Baldwin specification sheet where it talks about netting.