Sound is better when I stand up?

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?

I was talking about the electrical phase at different frequencies that are shared around the crossover region between the tweeters and woofers, not one speaker being wired out-of-phase to the amplifier.  It’s a common issue with multi-driver speakers.