I don't know if you can generalize a sweet-spot for every cartridge with all the different weights and compliances out there. On an Ekos or Ekos SE I find the best thing to do is balance out the arm with the counterweight, dial the tracking force dial to the recommended tracking force, or to the middle of the recommended range (in the case of the Etna it appears that would be 1.67 grams), then using a digital scale readjust the counterweight so that the actual tracking force matches what is on the dial. After that dial the anti-skating to match if you have an Ekos SE/1 or SE with a little bias when set to 0, otherwise for older Ekos SE and Ekos 1 and 2 go about .3 grams above the tracking force.
Once you have achieved that listen to it and then try above and below the starting tracking force to see if it gets any more musical. If it is more musical at 1.72 try it at 1.70 to see if it gets better yet or worse. If worse try 1.75 (even if it is a little above the recommended range). Keep trying until you find the most musical setting, one or two hundredths of a gram can make a difference so don't be afraid to try them. When that has all gotten into focus then do the same thing with the anti-skating. The effects are more subtle but still audible, I find especially so on voices.
As an example I have found the Ekstatik to be most musical at 2.1 grams despite being recommended for 2.0 and the anti-skating at pretty much 2.05. With a Kandid or Krystal I find 1.75 for both tracking and anti-skating to be most musical. I think you will find with most cartridges that the counterweight will be a little back from the bearings - probably 2/3 to 3/4 of the way towards the bearing housing from the back of the stud. But always trust your ears and don't be afraid to try settings that are a little different from the manufacturer recommendations.