To be honest. Im a bit confusing seeing how bookies favoring intermilan rather than ac milan. i do know that if playing away or home won't give impact as the match will always be happening in san siro soon. Intermilan was just winning with lukaku has been showing his great performance again.
What you have said was also true if milan is above inter right now. I may also think of picking ac milan rather than intermilan.
Yeah most likely, there are many factors that determine the club is favorite or underdog, head to head are one of the factor. But San Siro is the AC Milan's home, if Inter Milan play, the stadium is named Giuseppe Meazza.
I still don't agree AC Milan will able to beat Inter Milan, Inter Milan is well rounded club while AC Milan only relying Leao and Giroud. Giroud is currently injured, so that's might the behind reason why AC Milan is underdog in this match. But Giroud is expected able to play in early May, maybe the odds will be changed when the date already closer with the match.
Now they are not in a good state in Serie A, and AC Milan is still slightly better than Inter Milan. However, the Champions League matches will be very different. The preparations they have made still have time to make changes to their form of play. I'm not too early to say who will be able to win, maybe I'll see how their last game was to conclude something, and try to bet on the match.