Thanks Dan for the illustration. And yes, pulling air through the top fins was one of the objectives. Though it was "fiddly" to make and fit to a flying airplane, it was very effective. On yesterday's flight, I would have expected to see that cylinder 50 degrees warmer than it was.
I am more than a little surprised how often you see baffling like this. I know it is up to the airframe designer to come up with the cooling system, but damming up the airflow on #3 (and #2, for that matter) seems like a significant oversight. Seems like the Z bend in the baffle should be lower on the cylinder so the bottom bend is not adjacent to the "zero fin depth" region. Following the plans, the lower shroud serves no purpose... In fact, you would likely be better off removing it so all the fins could at least radiate.
Also, should have checked to see if this had been discussed on the boards before... I see that you have thoroughly illustrated the issue in the other thread (at least I got to bask in the glow of my own genius for a day...).