User blog comment:SlashZero/Spring 2015 E-6 Hard Boss Pre-final & Farming Composition/@comment-26363666-20150508084435/@comment-861160-20150512060903

You can swap the seaplanes between Jintsuu and Haguro for slightly higher activation chance. Also if you have any 20.3cm(2) or 20.3cm(3) I would upgrade them at least once and use them over 15.5s.

Other than that... craft another AP ammo or at least get a Type 32 Surface RADAR for Yamashiro, perhaps? Besides the obvious "get Ooi" suggestion the only other thing I can think of is go with 3 torpedoes on Shigure and roll the dice harder?