Played with some testing this evening, which produced one strange result: clearly at "0" adjustment, focus is extremely far off. Changing to a setting of -5 results in a huge correction; changing to a -20 is quite an incremental, but noticeable, change in comparison. I can easily see the focal plane shift from -5 to -10, -15, -20.
First round indicates I should be between a -10 and -15. I didn't attempt to get any more granular (ie, no -12, -13, etc) on this round.
I'm planning on just enjoying taking some pics tomorrow with -15 dialed in. I'm pretty darned sure that I'll get keeper images; there might be some room for improvement, but I'm not in a rush.