[JJ_SO]

Just say goodbye to the idea, the DoF range is a range where everything in it is a precisely sharp in focus as you see the things you put the focus right on. As you said, it's hard to see, but can be measured in theory, if one is defining the "sharp enough" appearance. You might want to look at various test results here in Photozone in the last column of a lens test where they do the analysis. Often you see a ruler and above aperture numbers. By hovering the mouse over the numbers the picture changes. Here's a sample of it 

 

Now, the question is what is sharp enough for you? If you really want maximum sharpness in a given range, focus-stacking would be a (time-consuming) way to go, at least for not moving subjects.