[Trevally.]

You can adjust the thermal layer here:-

\data\Cfg\sim.cfg

[Sonar]
;how long you have to be in the AI's active sonar cone before he will start pinging.
Detection time=2.0 ;[s] was 5
; lower values than 1 make it harder for AI to detect you
Sensitivity=1.0 ;(0..1)
Waves factor=0.3 ;[>=0]
Speed factor=15 ;[kt]
;how much surface area you present to the AI for him to ping off of, before he gets a ping
;think of this variable as to how much "slop" you can have when pointing your bow or stern at an approaching AI to minimize your profile
Enemy surface factor=325 ;[m2] was 520, decreased by 35%
Lose time=15 ;[s]
Min Signal Strength=0.125
Thermal Layer Signal Attenuation=1.75 ;[>0], 1 means no signal reduction, 5 equals signal reduction to 20% was 5.0, decreased by 70%