User blog comment:Shinhwalee/Major Event Preparation Guide for Admirals/@comment-1365426-20151110102302/@comment-24930367-20151110105252

Yes, 90mm is a HA-gun with built-in fire director, but the problem if you used 90mm + air radar setup is that the AA cut-in is much weaker, about half as strong as her strongest cut-in (not to mention lower rate).

I suggest you to read this page. Concise enough to get all information needed.