So you know from reading Ethan's info, your diagonal setup is not optimum. Obviously that center post is what causes you to choose the diagonal. I have the same problem Another minus is the equal sides at 16 feet but you got what you got. Your 4 foot deep trap and other corner traps will help and you may even want to add wall/ceiling traps (maybe wall/floor too) in the space between the rear and side corners.
A cloud above centered between your speakers and mix position is always a good idea too.
Hi - yes I agree with Rock - a cloud panel over your mixing position will be beneficial for first reflections and if you want to address the side first reflections you may consider using two Gobos (portable acoustic screens) one either side of your mixing position.
The pillar at the center is a problem and can not be moved. I'm going to wrap few layers of light fabric on it.
I live in an Earthquake zone, 400+ earthquakes(after shock) in 1 year. That is why heavy things above my head is not possible. Thus, I use light fabric, air breathable fabric, few layers of them which makes 3 or 4 finger thick size.
I hung the fabric by using fishing plastic thread. It starts from back of speakers to back or my head; the fabric is above my head. 2 or 3 feet above my head while sitting position.
Fishing thread makes semi circle, because of gravity the center part of fabric is lower than sides. It make poly-cylindrical shape and it is like a spring.
I'm not sure if it can be called as a "CLOUD" but it is the best I can think at the moment.
Bass is punchy and details can be heard.
Nigel Spiers, I've portable movable cotton filled 2 piece; 4 feet x 3 feet at my right and left. And, on it's back side I've 2 wooden curtains [arabian wooden curtain with hundreds of holes] at right and left side, making around 10 degree slope. Making right and left not parallel.
I've 3 PRD on my back, around 10 feet away from mt back.
The problem with facing a corner is that puts a large focusing corner behind you. But when facing a corner really does make sense, and it might here with that post, the rear corner problem can be reduced by making the entire area absorbent. That's useful even with a flat wall behind you too!