Have you tried increasing the "Aperture Edge" above zero? I haven't used the focal depth much, so I am unsure what result is expected, but in order to get any response I have to increase the aperture edge to .1 or above. Then you can play with the "Aperture" number. Strangely, with the aperture set ...

I noticed that as long as I made a Sketchup "scene" out of whatever view I was rendering, whatever Octane plugin settings I revised/selected were saved automatically back to the "scene".

For example, I set my view up in Sketchup, save it as a scene, open the octane render window, change kernal ...