Air flow metering valve test parts

After getting caught up on some work around the house I finally got to getting some work done on the furnace. I made up test parts for my idea about varying the air flow my furnace is getting from a shop vac. I could just buy a cheap hair dryer and be done with it, but I already have the shop vac.
I took the pipe that fits into the tuyere and added a small stop so that it would slide in but not protrude all the way into the furnace. Then I cut an opening into the pipe, made a small sheet metal finger that would fit into the opening in the pipe, obstructing a lot of the airflow up and out before it gets to the furnace. It seems to work so far. So far I have only roughed this together. After testing during a firing of the furnace I will clean up the design and construction, if it works as I expect it to.
Here is what I have done so far: