While the main post is tilted, the camera mount is also angled to account for this angle. Thus, as the camera goes higher up the main post, it remains perfectly perpendicular to the base board (and thus the coin). What Ray was saying (I believe) is that as the camera traverses the tilted main post, the higher it gets, the deeper on the baseboard it focuses (the part of the baseboard on which it is focusing is farther toward the back).
As Ray pointed out, the hand crank on the main post is not useful for fine focusing or for stacking shots, but I had no intent on using it for that. His description was best, the hand crank is used for "coarse" tuning (e.g., the height difference between a 75mm lens and a 135mm lens), whereas the focusing rail of my Pentax Auto Bellows will be used for fine focus adjustments and for taking multiple shots for a focus stack.
One thing I did do tonight was molded a small piece of polycaprolactone (thermal plastic) into a thin wedge so as to keep the camera mount from creeping up during imaging. Because there is constant tension from the spring-type metal ribbon at the top of the main post, the mount wants to creep up instead of down on occasion. This little "doorstop" type wedge keeps the height fixed for multi-shot imaging. I'll keep playing and let you all know how it works.