I think that they have taken sandbagging into account by comparing your results to the ratings of the drivers around you. Meaning that a top position amongst slower driver with lower ratings, would result in a lower rating than a midfield position amongst top drivers. Of course there is a crossover though. But the opposite scenario would also be annoying. Say that you are a slow qualifier, but quick in race, then you might have a hard time actually qualifying amongst people that in race pace match you. In some instances the dividing into splits might be nice to have, not based on qualifying / hotlaps.