As an alternative to 1) you could increase the reporting range of mapcontacts:
"Display Range To Opportunity Radio Contacts" or "Display Range To Important Radio Contacts" in Sh3/data/cfg/contacts.cfg
I'm not sure what the diference is between them though. Probably "Opportunity" are lone vessels, and "Important" are convoys.
Getting a contact reported still depends on chance. But the game doesn't limit them based on the range to your uboat.
[Edit]Some time ago I worked out what the best hydrophone interval was to not let a target escape your attention. Or atleast with minimal chance.
http://www.subsim.com/radioroom/show...7&postcount=27