After what told at
Pacific campaign strangeness, eventually I found a work-around editing mission by Full Mission Builder and reducing both japanese and american trip by moving furthest waypoint of the former closer to its airbase and same for first waypoint of the latter. In short, they now meet near japanese airbase and FIGHT, instead of RTB stupidly. Finally, a bit of fun!

S!
GB
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Ardisco, colpisco, meninfischio ("I dare, hit and do not care about it!" - Written on a SM 79 "Sparviero" during Spain civil war)