I wonder how much is calculated, and how much is empirically-determined? For example, the 40mm f/2.8 pancakeis down in group D (center dual cross only, no outer columns of f/4 points) - does that mean the virtual aperture is actually in front of the physical extent of the lens?
The 40 wasn't on the list last time I looked, because it wasn't yet out. Hrm, I can't think of why that one would be where it is. I think there was an old 35-135 (or something like that) which didn't make any sense, either. I'd have to see one of these pancakes to come up with a guess. Off the top of my head, the only thing that comes to mind is that it has something to do with it being a unit-focusing lens.
I don't think they need to figure these things out empirically in the year 2012. I'm pretty sure they know in the design stage.