DOF shaders don't work well in Quake 2

All of the DOF shaders either detect the whole screen as the background (farther away) or only detects things 5 feet from my face as the foreground half the time. Is it just Quake 2 being an old game? Did I do something wrong?

In the ReShade compatibility list Quake 2 has a 'perfect' rating so I guess that should work.
DOF shaders rely on the depth buffer, so first enable the DisplayDepth shader to see if that works correctly: you should see a greyscale image with near objects in black and far away objects in white.
If you see only black or white, try changing the values for the depth buffer input (in the settings tab from the ReShade UI):Set RESHADE_DEPTH_INPUT_IS_REVERSED to 1 or 0 and/or RESHADE_DEPTH_INPUT_IS_LOGARITHMIC to 1 or 0.
After you change a value reload the shaders.