The cable length can be up to 18,000m which complicates position of the actual TPL
It is very important for the operator to know exactly where the towfish is in relation to the surface vessel. The computer system onboard calcs the towspeed, cable length, catenary arc in the cable, and data from the towfish so they pretty much know exactly where the fish is.
Many actually actively ping the surface ship to coordinate surface ship coordinates with their offset and IRU.