Having used this for quite a few shows now, I have to say that I have yet to really figure out the level meter. What seems to be true though is 0db is peaking at the right of the meter where you would expect it to be.
Having said that, I think that the meter is fixed in that no matter what the mic gain setting is on the back, the level scale doesn't change.
Finally, for reference, I've been running my levels VERY conservatively. With my levels peaking a little over half way on the scale, I seem to be getting about -15db peaks. So, again I think that confirms that the mark on the meter is -12db point.
Look at the meter scale and you'll see the mark I'm talking about...I don't have a key on my keyboard that corresponds to the mark, but it's the same symbol as this '^' only it's pointing downward.
NOTE: For clarification, the meter is a logarithmic scale. When I refer to 'half way' above, I mean when my levels are peaking physically a little over half way, so my 'half way' reference mean LINEARLY a little over half way.
I hope this helps.