Hi Branden;
First-generation Batchboxes (the most common type) use a primary air supply at the door and a secondary air supply that brings fresh air to the rear of the firebox, directly in front of the riser port.
The secondary air mixes with the volatile wood gases, creating a flaming vortex inside the riser, often called a double ram's horn.
The RA stub is a replaceable part of the secondary air supply.
On my extreme burning shop stove, a
carbon steel stub in this location will last apx six weeks before spalling apart.
The cast iron griddle was an experiment to see if it was a viable alternative for a batchbox roof material.
For my stove, which runs exceptionally long and hot, it failed miserably.
As the roof on a casual use batchbox (ie, two lightings a day), it is proven to last.