With TMO, not sure about stock, but probably so, escorts are doing one of two things, pinging or listening. Basically if they're moving they're always pinging, but only pick you up if you get in the sonar cone. Why in the cone, it depends on many factors how well they have you pinged..which you can tell by the sound..You know when they speed up over you, they're making a run..If you're deep enough you can haul arse and the charges will fall behind you.
Fun to play with the cams off and not see what they're throwing....
If you want to understand TMO's AI...Ducimas explains well..
http://www.ducimus.net/sh415/ai.htm