Lower the wave factor, or attunement, i forget which.
See thread in mod forum on, "getting rid of pinpoint drops".
(edit: AH HAH, found it! I did alot of testing on AI passive and posted my results in it)
http://www.subsim.com/phpBB/viewtopic.php?t=45370
AI doesnt normally start active sonar unless they had a passive contact first.
The AI's Passive contact is like....... by default.. nearly deaf. . How large the waves are plays a BIG factor in their detection.