Hi Alon - I have struggled with that issue as a well since I have never been to an in-person class. But to me the correct tension is the one that allows me to weave smoothly (without getting skips), and to get the sett that I want.
I am still trying to figure out the floating breast beam on my spring 2. I understand that it is to help us maintain constant tension throughout but I find it difficult to use.
However, I am currently weaving 8/2 cotton turned twill towels set at 20 ppi/epi and I am finding that using the 7th or 8th slot to give me good tension. I am sure this varies depending on the project/structure, etc.