I have done measurements before, and not yet after. Before, the rear plug boss temperature in this particular engine ranged from 120 - 145 degrees C , rich 6000 rpm >> max 6100 rpm, on verge of power loss, using a 3W 20x8 prop and MVVS 3271 in cowl muffler (82 dB(A) @ 7 meters)
I was aware of the air stagnation at the rear. For that reason the baffles closely shroud the fins way past the cylinder center line, so they converge like in full size radial engines. The wedge idea may be very good. Anything that causes stagnant airflow swirl is to be taken care of. Maybe have different exit angles in the baffles, so any stagnation occurs after the cooling section.
To check cooling in a lean set engine for best power, I did take out the cylinder lining to check heat coloring. There was no liner discoloration at all, and the liner outside surface was oily/slippery without any signs of oil baking in the hottests section above the exhaust port. The piston was clean in the colder parts, and showed slight carbon in the hot parts. Piston liner wet with oil and slippery. Ring land above ring slightly black with soft soot.
Also, the engine did not have the typical very slight rpm drop that hot gas engines normally show after a few laps in flight.

I cannor repeat the same measurements, because I had to change my setup to comply with our club's 80 dB(A) requirements.
New data: 7100 rpm using Mejzlik 20x8 and 3W smallest canister (stinger reduced to 6mm ID) 79 - 80.5 dB(A)@7 meters. Thrust is in excess of 9 kilos (20 lbs) .my 9 kilo tow plane goes straight up with this setup.
I will take some more measurements asap and post.