Open up your sim.cfg
In it you'll see a block of text for controlling the escorts sensitivity.
It'll look something like this.
[Hydrophone]
Detection time=2 ;[s]
Sensitivity=1 ;(0..1)
Height factor=0 ;[m]
Waves factor=1.0 ;[>=0]
Speed factor=15 ;[kt]
Noise factor=1.3 ;[>=0]
Thermal Layer Signal Attenuation=3.0 ;[>0], 1 means no signal reduction, 3 equals signal reduction to 33%
Min Signal Strength=0.2
[Sonar]
Detection time=5 ;[s]
Sensitivity=1 ;(0..1)
Waves factor=1.0 ;[>=0]
Speed factor=20 ;[kt]
Enemy surface factor=520 ;[m2]
Lose time=30 ;[s]
Min Signal Strength=0.2
Thermal Layer Signal Attenuation=5.0 ;[>0], 1 means no signal reduction, 5 equals signal reduction to 20%
Change Thermal Layer Signal Attenuation to 1 to disable the effects of the layer.
DISCLAIMER: I have no idea how seriously this is going to effect your game, as I have not tried Nisgeis' AI mod.
I'm just telling you how to do it
EDIT: I know of no way of altering the depth of the layer.
It may be possible. Who knows?
(Wasn't in SH3 or 4 though)