It is the partner airline that decides how many AE miles it will give for its various fare levels, not AE. If Varig has two business class fares, just as AC does, then it is unlikely to give the same mileage for both, and thus you'd get a lower mileage [i.e. 100%] for discounted business and a higher one [i.e. 125%] for full business class. Afterall, the airline is not getting more money from you, so why should you get the same number of miles when you've already received your bonus in the form of a discounted business class fare?