Found this study that clarifies 2 aspects of narrative engagement : spatial immersion (in fiction imagery) / identification with the character (alignement with their goals).
The problem is that, equipped with that knowledge, I can only find justification of my preferences (see below). So the question is : can you bring different viewpoints to help me out of this subjective ditch ? I think miniature users have something to bring to the discussion.
Identification is empathy, and brings actual changes to the world (eg Indra's daughter scenario for Misspent Youth). What part of Dirty Hippyness it adresses is self evident.
On the other hand I find spatial immersion a problematic goal for a TTRPG.
First, it's hard to get. It requires mostly verbal material, as in LARP or ritual + dialog : the manipulation at the table contradicts and dissipate fiction imagery. And I am never satisfied with it : I picture one location here or there, but the characters and the story only coalesce into images the day after, like with dreams, mostly by reinvention.
Second, it's easy to understand how it leads to spatial murk : by essence, the imagery is highly personal. So what you do ? If you use a map, you're back to square one.