Not the water level that the skimmer sits in that should be 5-8", 7" being ideal ime for most skimmers. I am talking about the water/bubble level inside the skimmer. Tune the skimmer so the water/bubble level is about 2" from the very bottom of the collection cup, let it run like that for 24 hours. Then tune it from there. In the vid you posted I can see the water level is up inside the cup neck. If you look you can see a dividing line inside the skimmer where the water turns into all foam and bubbles, that line is the water level. I hope that helps.
Edit to add pics. Here you can see the wayer bubble level on my skimmer and this is skimming dry, sump water level that skimmers is in is 7", 2 days of skim.