The A/D settings are a volumetric calc for the min/max sender resistance...and I'm honestly lacking the mathematical prowess to explain it. A/D counts are a unit of measurement or "hits" in a voltage range. So if a sensor uses a voltage sweep of 0-5v, its a A/D count range of 0-1024 (I'm sure there is a divisive reason why, but since it yields 204.8 counts/volt, I can't give you a logical reason).
Modifying that is like using a variable pot to modify voltages for fuel cut on old FI cars.
The A/D count of 20 is roughly 1/10 of a Volt, sweeping to 7/10 of a Volt. I suppose you COULD flip them, and see what happens.
Potentially you could also open the Level VS Volume table and flip the first and last cells, then use "Interpolate" to fill the scale in reverse.
A/D count is used about 50 times once your deep enough in a few tables.