Bass only when I stand up…

The quickest way, not the only way. Some of the suggestions will help. First pull your speakers out from the wall. At least 500mm, next add subwoofers. If it's not in the budget pick up 2 used woofers for the time being. As you know bass is non directional, adding more fills the nodes in the room and helps equalize the bass in the entire room. It isn't about getting more bass,  you are simply filling the nodes in the room. You may have to turn them very low to help from disrupting your main speakers, but it will work. Good luck, Tim

Sorry 500mm more. 3 1/2 to 4ft total distance from the wall

Just get a booster chair 

Where the heck did my last response update go?

Well, good news.

I took the advice here about moving the speakers closer together. I moved them about a foot each side towards the centre and about another 6” forward.

Problem solved.

Now there’s no difference standing or sitting. Both have the same excellent bass. Powerful, deep and clear. Wife approves! She’s a long term Hi-Fi buddy.

I have them towed in towards the seating position and it’s a nice clear focus. I’ll bring another eames style chair in this room shortly. Or an exercise bike!

First, thanks to those here who suggested this solution. It worked. I’m grateful.
To Erik and others here who provided detailed analysis and thoughtful suggestions I appreciate your efforts. Maybe these are constructive suggestions for the future.
​​​@danager try closing the gap between your speakers as a starting point as much as you can. Let us know what happens or what obstacles you have.

John

Bass response is one of the craziest things in hifi.  Over the years and living in different houses with varying room sizes and volumes I would stubbornly set up my stereo with the same separation distance between the speakers and distance from the front wall.  I would notice that the bass would often sound better in the back of the room than in my listening chair.  The real head scratcher was when I had great bass while standing and it would all disappear when I sat down.  Finally, in desperation I moved my speakers closer together and Bam!  I had bass again.

The bass response relative to speaker position seems to be a function of bass driver size, room shape and volume.  If the drivers are too far apart the nodes rise upward and outward.  That is the part I did not visualize- the 3 dimensionality of the bass response until I hit on it.  The good thing is, or what I found is that the bass remains the same when moving the speakers closer and closer together once at the sweet spot.  So it is possible to attain the largest soundstage possible and have great bass by just finding that sweet spot for the bass. 1 inch or less movement of the speakers makes a difference.