Interesting! I tried the 50 with the 24 reversed, but for some reason got a huge amount of vignetting when I stopped down the 50. It was fine as long as the 50 was wide open, but I wanted more DOF. I couldn't understand that at all, since I was stepping UP (the 50 is 49mm threads while the 24 is larger) and the 24 was wide open. When I was using the longer lenses I only got vignetting with the 1.7 when it was stopped down a bit. the 100mm lens I was using was at f22.
I really should shoot a ruler, like you did, to see what magnification I do get. Your examples are really well done.