If you add a port to an  Eclipse configured  PL (conference) so that it can contribute permanently, you will ALWAYs have the in-use tally active as there is always a talking member, regardless of the audio on that line is silent or not.
One way to trigger this tally when audio is present is to remove the port from the PL and make it talk through another method.
Create a new Route, give it a sensible name, and make the source your port, and destination the PL.Create a new Control and name it something sensible that you can find later. Attach the route you just made to the control Go to Hardware > Cards & Ports, and attach the new Control you just made to the VOX action in your port.
Whenever any audio of note appears at your port, it will now trigger the route you've made to add it to the PL, meaning the in use tally only comes on when there is someone actually contributing to the PL.