Foolishly, I built a house west of my place of employment. This means that for several weeks a year, I drive with the sun in my eyes. This morning, for instance, the sun was right at the horizon as I drove toward it. I can guarantee that a "a thumb over the circle" doesn't help very much if there is the least bit of haze, scratches, or moisture on the windshield. I suspect that plexiglass canopies might exhibit quite a bit of the same sort of glare.
That said, the initial WB sun glare effect was terrible. I would hate to see it duplicated here. However, I wouldn't mind a bit more "invisible area" near the sun than what we have now.