Contender, you have been doing research obviously on delivery of the gas to the forge. Me, just bought a kit from
http://www.hightemptools.com/supplies-mainpage.html
My forge is round like yours, and with that Bubble Alumina you can just put a angled groove into the Bubble Alumina once it is "troweled" into the forge bottom to allow the flux to flow out and away, perhaps into a reservoir of your design or even out the bottom somehow. The groove will not affect the airflow or should I say the rolling of the flame. And it is highly impervious to flux. I even lined my front and back openings with it since Satanite was proving to be much too fragile. Great stuff. I just don't think a lot of folks have much knowledge of it yet. Check it out here:
http://www.hightemptools.com/refractorycoatings.html
I bought the 2.5LB bag. These guys were great when I bought my forge materials. They even have glass platens for your grinder and wrought iron anchor chain and cable for cable damascus if that is of interest. You probably already know of them.
Please post pics of your forge interior whatever you do. Any forge knowledge passed on here will help a lot of people. Good luck!
Tony Z
Kansas City, MO