soundstage location~speaker plane; speaker design or placement?

Look up "Head related transfer function" or HRTF for a more complete explanation.

Partly this is timber. An upper midrange emphasis may make the soundstage appear closer to you. I use a very relaxed, sloping off curve that sometimes make it seem as if the speakers are too far back.

But quite a bit of this is rather fine response ridges and valleys in the right spots. Some Wilson speakers have a 2.4kHz dip, which is known for accentuating "imaging" overall. See the latest Stereophile review of the Eggleston Works Viginti:

https://www.stereophile.com/content/egglestonworks-viginti-loudspeaker

Pay particular notice to the FR comparison between his Wilson and the Viginti around 2.4kHz and how the reviewer discusses the difference in imaging.

Generally speaking though, room acoustics also play a large part in how well you can discern any of this. I have found that adding room treatment in the plane (x, y or z) of deficiency greatly enhances that. For instance, if your imaging seems very flat horizontally, adding carpets and treatments in the ceiling may cure it.

As always, buy what you like to listen to. 

Best,


Erik

No idea how they do that voodoo they do do but no doubt it’s a combination of all 3(design,room & placement)...