Sound is better when I stand up?

@simao 

I know what it’s like to work with a small room- you can see mine under user/systems. The tweeters in my speakers are above my head while sitting and it’s no problem. The image is centered and at a nice height. At first I would say to move a few inches further back but it sounds as though you’re very close to the wall already. Needs further examination 

holmz no headrest, but it is a wingback. I wonder if that’s an issue

@simao
What is a wingback?
Is there a image of the model of chair?
(If there is some place for sound to bounce off of it can cause a problem.)

Have you tried a simpler chair, like a dining room chain, in the listening position?

Try standing up and moving rearwards so that your back is against the back wall… Does it also sound similar to the sound in the chair?

It's the wingback!

move a short back chair in same position, see what difference!

Have you treated your ceiling with acoustic panels yet?

+1 jond.  With most speakers your ears should be at tweeter level to sound as spacious as intended.  Have you tried tilting the speakers towards you or raising your listening chair?