Faint odd radius halos
Now here is an example of a display where you see nothing special visually. Just a faint 22° halo that is a bit brighter from the top. But there was one visual clue, however, that revealed it might be an odd radius display. It was the broadness of the 22° halo. And indeed, in the photos 9° halo is seen as well as 18/20° halo. The outer halo might not contain 22° halo at all, rather, it can be 23/24° halo.
Had I had a convex mirror, the 9° halo would certainly have showed up with it, also the 18/20° halo. The two photos above are versions of one. They are 2 minutes stacks. The date is 28 April 2011.
The display just continued and one could have gotten several hours stack of it. When in the afternoon 9° halo was visible to the naked eye, I took another stack in the middle of tyre changing. The third image has 7 frames taken during about 2 minutes. There is 35° halo (arrow), it is seen also in single images, which means it would have been observable with convex mirror. Fourth image is a bit longer stack. Now the 35° halo is on the other side.