DD's sensors + depth checking

I was testing depth cheking and DD's sensors on this action in single mission "Sink the Coregeous" made lots of pings but there seems to be no reaction from destroyers at pings from my u-boat.
Correct me if I wrong but as far as I remember in GWX manual there was something mentioned that this ping by cheking depth with sonar or tracking the target while submerged could be heared from miles around. Has anyone else noticed the ignorance of DD according to sonar cheks of u-boat ? :hmm:

And please, somebody change my avatar now, omg