By golly, I tried that and it does indeed work. I stand thoroughly corrected and better educated than before. I can't believe that years of school (much of it in photographic technology) and more years of working hadn't taught me that.

I'm still thinking about the apertures larger than f1.0 but I have a feeling you're also right, that it's the effect of packing the larger area of light into a smaller area. Not exactly amplifying the light but creating the same effect.