about hydrophones
 

I understood KDB can only make contacts while submerge since its on front and at top of sub, but Balkon Great is at front and on bottom of sub in the water, why cant it pick up contacts while the sub is on the surfaces? what about Prinz Eugen, the heavy cruiser which can pick up contacts while on surface using hydrophone, Im not sure which type that cruiser used? What about GHG, is it on front and both sides of the sub in the water, even while on surfaces? Balkon Great hydrophone that is already in water but it still could not pick up any contacts when the sub is on the surface unless the sea is rough as it tend to pick up contacts baffles me. Wondering if its the game programmer's error or bug for this game or is it normal as real it was back during Uboats' years?