The skimmer in first chamber with drain from tank is a good thing. It gives the skimmer first chance at the dirtiest water.
Not sure what you're saying. If you turn the skimmer 1/4 turn clock wise...
Than not only will the skimmer pump's intake be away from the tank drain pipe as it is now,but the skimmer output will be closer to the drain and will both be away from the pump intake, as well as far away from the water that leaves the chamber. Less air bubbles and turbulence should make the skimmer more steady.
Sometimes ppl misunderstand that more air going into Venturi makes the water level inside skimmer lower. With more bubbles but lower. Just take the air intake hose and stick it under water and you'll see what I mean.
To me the most air you can get into the mix through the Venturi, and than adjust level inside skimmer with output valve is in most cases the best you can do.
If I were you I'd start from scratch. Put the cleaned skimmer right in the middle of the recommended water level, give a day in between adjustments to try to dial it in. If after some time you can't get it dialed than I'd try this mod...
Get a short piece of tubing that fits over the Venturi where the water enters. The longer the distance from where the air tubing tee's in, to the end of the pipe where the water enters, the more air that will get pulled into skimmer. A lil bit will make a big difference. Again, the more air that goes in, the lower the water level will get, so the more closed the output will have to be to get desired skimate.