I made a test, seems to work properly by now.
I created a mission with 2 convoys looping. 100 km away from each other.
The escorts passed over the sub without detecting me, i then ordered ahead flank to make some noise, i got some pings, dived to 400 ft below thermal layer and escaped. Next i go to the other convoy location and the escorts the same, the didn't detected me when passing near.
However the escorts don't give up just in a few hours, may pass half a day and they are still on alarm.
For now i have doubts what happens if you are detected by aircraft.