DOF too deep(not blurry)

[fixeighted]

Whatever your system units are, make your display units mm and create camera and set parameters, just so you don't have to use confusing silly values, and you should be good to go.

[vasil.minkov]

So I'm not following anymore. Can someone recap with a simple enough example?

I work in centimeters and sometimes in meters, my scenes are set up from the start and I'm not merging cameras from different scene units.

For instance: If I need a real life camera with F set to 2.8, and I create this camera in a centimeters scene. Do I need to set the value to 0.28 instead or did I miss the point of this thread entirely? And what about if I work in meters? Is it 0.028 then?

You should set your F to 2.8, regardless the system units.

You may use any system unit. But the system unit decision should be your first step. When you start adding physically accurate objects in the scene - your system unit of choice is locked to what you have started with.
And if you want to switch the system unit for some reason then you should re-size and reposition all scene objects accordingly, in order to preserve their physical size and position.