just a tought, I have lots of bass traps in this room, and behing the thin surfaced walls on each side of the desk I have tons of rockwool from floor to ceiling with a large hole covered by speaker fabric... maybe that's why my low end is acceptable ?
In fact now I feel that my no man's land is after 300hz.
And the graphic does'nt look good, even in the 600-1000 area. There's no smoothing on the graphic but antway, my ears don't lie, at least I hope so...
Yes, you traps must be helping a lot. I think the next test should be on the back wall. It seems to be very close to the operator. Can you place some temporary absorption panels on the back wall and measure again? 400Hz is 2.8 feet long and is 2.25 feet. - It looks like that big dip is about 480Hz which is equal to 28.2 inches. Have a look for something(s) at this distance. Or it could be a harmonic of 240Hz (56.4") or 120Hz (112.7")...
I'm not quite sure on "how it sounds" because I had to change my monitors last week (tweeter explosion due to power failure) and I have to get used to the new ones. I'll make some tests just to be sure.
I deeply regret the outboard rack in the middle of the room and it's way to high... but after seeing so many pro studio pics with that kind of rack I tought "why not ??" and it was difficult to put it somewhere else.
Well at least the room is good looking and everything is in it's right place.
All my best