Joe,
The picture is a little deceptive. The upright sections, let's call them dividers, are not parallel and evenly spaced, most noticeably at the top. Again, the picture for some reason was rotated 90 degrees when I posted it, despite repeating it a few times. If you were to measure the spaces horizontally between the dividers on the top section (where the cubbies are the smallest), you'd find that opening size at the top is not the same as at the bottom of the divider. And there is a little variation from one cubby to the next, though they were supposed to be identical in size. They aren't off by a lot (which may explain why it's hard to tell with the picture) but enough to be noticed.