Derek,
Cutting below center will cause a lot of problems, especially as you
get closer to the center. You have a vertical blade in a circular
kerf/hole. As you get closer to the center, pressure on the blade, and
pressure on the support (which will flex a bit) the tip will get more
below center as it goes in. I find a lot of the time that I am
supporting the tool, instead of using the tool support to keep the
cutter at center. If you have a catch below center, it will bind and
dig in worse, just like when turning a bowl if you work below the
center.
robo hippy