In that image the corners have a lighter strip, or highlight, as well. This is because the surface is beveled, the areas that are lighter face out at roughly a 45 degree angle while the larger planes are perpendicular - being at a 45 results in less occlusion. The larger you make the bevel, the less occluded, and thus brighter, those faces will be. From a rendering and physical accuracy perspective this is the correct result, and actually the first image is more accurate and correct. Though that is not what artists generally expect, which is why we added the uniform option.
The last shot you've shown is darker overall, which is probably a matter of gamma space. If you load your AO map as sRGB rather than linear you'll see darker occlusion.
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The last shot you've shown is darker overall, which is probably a matter of gamma space. If you load your AO map as sRGB rather than linear you'll see darker occlusion.
Here's some images with various settings
Uniform off, linear space:
Uniform on, linear space:
Unfirom on, sRGB (gamma) space: