About my misconception of your intent, my apologies. The general course of discussion here, leads one to be a cynic.
About how the optimization of sonar was done by Indian Navy. I have to say I am unaware of the technical details. The part I was talking about was mentioned in a book on the Navy, which is the official history of Indian Navy, called from transitions to triumph.
One of the biggest lesson IN learned in 1971 was the ineffectiveness of the ship based sonar in detection of submarine especially due to the tropical conditions around India. Even the Russian supplied ships were unable to detect them. This forced them to work on development of indigenous sonar optimized for the conditions. I know this may not satisfy your curiosity. But the fact that we are replacing the sonar in kilo submarine with indigenous, shows that the Navy has a lot of faith in it.
The rivers from the Himalayas are high silt, also causing higher salinity, multiple factors along with the ones you have mentioned cause the difficulty in detection