Frequency Response

I’ve recently started measuring my in room response and it’s become an entirely new learning process.  I’ve become slightly obsessed with smoothing out the in room response as much as possible through speaker placement and room treatment placement.  
Anyhow, I’ve got a dip in the response from 330-400 hz at my listening position.  The dip is not there when I stand vs. sit in this spot.  I’ve tried moving the speakers all over and I’ve tried fixing it by moving my acoustic panels around but I still can’t get rid of this nasty dip...

Does anyone have any other ideas I can try?  Has anyone here had similar issues with your room cancelling out certain frequencies higher up than the bass region we are usually talking about and what did you do to overcome them?
@newbee, definitely a null...  I just difn’t know or think that they happened above 100hz or so.  Never thought abkut hugher up frequencies cancelling themselves out.  Makes sense though.  I also didn’t realize how high of a pitch 300-500hz is.  
I tried some really big differences in speaker location and speaker height, even flipped them upside down and measured the freq. response.  Interestingly it didn’t change much.

I always knew the room makes a difference but now I am really beginning to see how much of a difference.  Its great to actual have a visual of my freq response now.
Anyhow, Im hoping to tame this and some other areas with more room treatments.  Maybe in the meantime I flip my listening position and see what happens 🤷🏼‍♂️
@erik_squires , thought the same thing. I put a panel on the ceiling right above and forward of where my listening seat is, right where 350hz was loudest.  Didn’t do much.  Then I took 2 panels from the front wall and put them on the ground in front of the speakers... Nothin.

It may just be this crappy little room Im working with.

Surprisingly my bass response is good.  0db at 28hz and -3 at 24hz. 
My response is pretty crazy / peaks and dips.  Just shows how much work my room needs.  I am actually hearing strange reflections when the program is playing this clicking noise in order to locate distances.

Anyways, I may work on it some more today and see if I can figure it out.  Wish I had some 25 foot runs of speaker cable.  I’d just move my speakers around...

I think it could be a camber, caster issue to fix it. BUT the reason is probably the XO point.  I fixed quite a few by tipping them forward or backward. It is usually forward for a dip in the mids, and back if the tweeter is boiling my ears AND I want a little better Mid Bass response.  Start with 1/2" and then go all the way down to shems. The chair idea is a good one to tune it the rest of the way..

Just remember, a little mojo goes a long ways.. Flat has never made me happy. It's always been a very slight frown, looking after tuning it the way I like it,  I hear what I like.. Slight rise in the middle. When I measure (not to often) it's always the same.. a slight frown on the PEQ. 2 db rise is just about right..

Cup your ears and see if it's what you like (chair forward call or EQ it.)

Happy hunting..

How about the floor between/behind the speakers??
It is a vertical problem. It is difficult increase volume in one area. Easier to attenuate volume.
If you put acoustic tile on the ceiling you will attenuate everything over 250 Hz and probably wind up with the same problem. It is called a "null."
If you have carpeting on the floor removing it probably won't help either.
The easiest way to fix it is Room Control. Check out my system page and DEQX.