HardTimes,
Great question! Most style guides only describe carbonation in terms of low, moderate, or high.
They do also use terms like moderately high?? I don't know the science the recipe calculator developers use to turn qualitative terms like these into quantitative numbers.
The books like How to Brew and Designing Great Beers do offer numbers when describing styles, but I don't know where they get them except their great experience in competition.
If you need to be competitive, I would consult the books, they were written by winners!
Good Luck,
Preston