The main reason is the very large number of real-life in-room frequency responses we have collected and analyzed over the years.
These teach us that we get a significant advantage in many cases with the type of positive gain offered by AutoCal2. Very often in rooms we see a low-Q notch in the range 100...300 Hz. We have analyzed that the combination of some positive gain used with other compensations in AutoCal2 results in more efficient compensation for this room effect without compromising either the quality of audio or the maximum SPL delivered by a monitoring system. There is monitor model specific restrictions to the gain, Q-value and frequency range of the positive gain filter to avoid problems with positive gains.