German radar wasn't any good until 7500 meters anyways, realistically speaking.
It was a night time and fog sensor really and most of the time the crew was afraid to use it as they feared being detected.
Remember what years we are in too.
More sophisticated radar came much later.
http://uboat.net/technical/radar.htm
Our boats only have the FUMO30 and 61, 65. 65 was useful to maybe 10 km against surface vessels (realistically). The devs set the 30 at 10km and the 65/61 at 15km, which inst realistic. That being said, I too find the radars sensitivity to be really bad too even with the devs given values. It can be and should be tweaked some.