[max-peck]

There is an entry for ship speed.

From Data/cfg/sim.cfg
(this is for TMO)

[Hydrophone]
Detection time=1 ;[s]
Sensitivity=0.15 ;(0..1)
Height factor=0 ;[m]
Waves factor=0.5 ;1.0 ;[>=0]
Speed factor=15 ;[kt]
Noise factor=0.35 ;0.25 ;1.0 ;[>=0]
Thermal Layer Signal Attenuation=2.0 ;[>0], 1 means no signal reduction, 3 equals signal reduction to 33%

[Sonar]
Detection time=5 ;[s]
Sensitivity=0.05 ;(0..1)
Waves factor=1.0 ;[>=0]
Speed factor=20 ;[kt]
Enemy surface factor=200 ;[m2]
Lose time=30 ;[s]
Thermal Layer Signal Attenuation=5.0 ;[>0], 1 means no signal reduction, 5 equals signal reduction to 20%

The speed factor value.
I'm sure I remember reading in a post somewhere ages ago that the speed factor value applies to the escort (not your own sub speed).
Of course I can't find that thread now, no idea what it's even called, so we'd need confirmation on this.

A little bit of supposition here.
I would assume that escorts going above the figure in the 'Speed Factor' line have their hydrophone/sonar effieiency reduced.
By how much? Who knows?