[popo]

I think you mixed up the image name - the greenish ones show the background highlights.

The purple ones the front highlights.

 

We might be using front and back with different references here. I was describing the focal point relative to the target. e.g. I focused in front or behind the target. I guess that would be opposite to describing the target relative to focal point e.g. the target is in front or behind the focal point.

 

 

What exactly causes the cut off in the shapes at top/bottom near the top/bottom edge? 

In one of the images you see the bottom being cut off when the highlights are near the bottom and the top being cut off at the top of the image, and the other image shows the top being cut off near the bottom of the image and the bottom being cut off near the top of the image. 

 

I think I mentioned it already. To me it looks like the rectangular area of the 5D2 mirror box doesn't allow all the real lens element to reach the sensor. The cutoff may depend on if it is focused front or back.