Oops, I've completely missed the last paragraph and thought that you were giving a wildly larger figure with a wrong assumption. Your actual assumption for optimally-efficient base-45 is correct and close enough to the actual QR code spec.
I’ve been adding bits to my comment as I went. It wasn’t there when you wrote your comment. I’m stopping now and going to go eat, confused about the 39% and 3% and what’s going on. I haven’t worked with QR codes enough!
