If you are dissatisfied with the way SH3/SH4 handles the passive detection (Which I also was) you simply need to adjust in sim.cfg (Plain text file, no special tools required) the values for all sensors general sensitivity to your liking, like I did:
[Visual]
Detection time=2 ;[s] ;was 0.5
Sensitivity=0.01 ;(0..1)
Fog factor=1.25 ;[>=0]
Light factor=2.8 ;[>=0] ;was 2.0
Waves factor=1.0 ;[>=0]
Enemy surface factor=350 ;[m2]
Enemy speed factor=15 ;[kt]
[Radar]
Detection time=1 ;[s]
Sensitivity=0.01 ;(0..1)
Waves factor=0.9 ;[>=0]
Enemy surface factor=5.0 ;[m2]
[Hydrophone]
Detection time=10 ;[s] ;was 1
Sensitivity=0.01 ;(0..1) ;was 0.04
Height factor=0 ;[m]
Waves factor=0.55 ;[>=0] ;was 0.75
Speed factor=15 ;[kt] ;was 20
Noise factor=0.2 ;[>=0] ;was 0.5
[Sonar]
Detection time=15 ;[s] ;was 10
Sensitivity=0.005 ;(0..1) ;was 0.01
Waves factor=0.6 ;[>=0]
Speed factor=15 ;[kt]
Enemy surface factor=100 ;[m2]
Lose time=30 ;[s]
Now I can also attack surfaced at night
