Why does bass have more “punch” when I stand up vs. sitting?

 Suggestions as to how to have the bass response while sitting as I do when standing?  

@lourdes  Sure- you want to look into something called a Distributed Bass Array. This is a set of subwoofers that allow you to break up the standing wave that you are sitting in. The subs have to be places asymmetrically in the room. They must not have any output above 80Hz or so; else they will attract attention to themselves. They can be fed by a mono bass signal because an 80Hz waveform is 14 feet long; by the time your ears can even acknowledge the bass in most rooms, the bass has bounced off of every surface in the room, meaning its entirely reverberant.

The best subs for this purpose IMO are the Swarm subs made by Audiokinesis. They are designed to be as innocuous as possible- they are designed to sit inside the room boundary effect (IOW right against the wall) and so give bass flat to 20Hz. They have garnered three Golden Ear Awards to apparently others think they are pretty good too.

@ditusa - Thx

Room acoustic treatment is most important thing, and a small portion of Hi Fi enthusiasts takes care about it.
I always say - start treat your room at proper way, upgrade it in small steps adding absorbers and diffusers rather than selling the speakers to buy more expensive ones, or buying concert hall amplifiers to prove yourselves that I have bigger and stronger d.ck than my neighbor.
Just follow few basic things in your room treatment from people that know their business:

https://gikacoustics.eu/?gclid=Cj0KCQjwlOmLBhCHARIsAGiJg7nWjJmqN91NALm-aCYxJR0zlkci-s5K7B-NSf-KKc1zU...

https://ssteu.com/acoustic-tube-bass-trap-copy-2E_AUvgHRMDR4S77zrTGl

https://www.rspeaudio.com/ASC-IsoThermal-TubeTrap-11-p/asc-tubetrap-11.htm

Enjoy the sound

Regards
Klikoman

You are sitting in a bass null.  So am I, but since it's a family room and there's not really another way to situate the sofa, there's not much I can do about it.