It sounds like we're trying to modify the recording because we aren't satisfied with the way it was recorded. Plenty of ambience, don't want my room's reflections added. Not enough of the hall, need to add my own. Etc.
Your post brings up something which is arguably a nuanced distinction, but imo worth taking a look at.
When done right, from a PERCEPTUAL standpoint, imo you're NOT adding "adding your room's reflections". Instead, you perceive "more of the recording" and "less of the playback room."
Let's look at Matt Hooper's descriptions, and I'll bold the key phrases:
it sound like the acoustic of the recording has expanded more to life size, and with eyes closed, the recording doesn't feel "canned" but sounds like I'm now in the same hall as the recording.
On good recordings it takes very little effort to sink in to the illusion of listening to a real orchestra.
As I said, in my room, adding a bit more room reflections can make the sound feel less "recorded" and a bit more "real" like being there.
Now does it make sense that adding more of Matt's listening room signature, via increased reflections, would have the effects he described? Nope. The reflection paths in his room are WAY too short to remotely begin to mimic being in a real concert hall. There is no way that the perception of "being there" is an artifact of the acoustic signature of Matt's room.
So, WHERE are these cues coming from? THE RECORDING! They cannot possibly come from the acoustics of Matt's room, unless he has a room the size of a concert hall.
What I think is happening is this: Matt's room is presenting the ambience cues on the recording in a manner which allows them to dominate over the "small room signature" of his listening room.
You see, there is a competition between the venue cues on the recording (whether real or engineered or both) and the playback room's inherent "small room signature" cues. Normally the latter dominate, but if we can minimize them while still effectively presenting the reverberation cues on the recording, the venue cues can dominate, assuming a suitable recording.
Even under the best of two-channel home audio playback conditions the ear will be presented with a poverty of venue cues, so it is not trivial to tip the balance enough that the "threshold" is crossed and we have a "you are there" presentation. It takes some fine-tuning. But when the ear/brain system accepts the recording's venue cues as being the more plausible package of cues, perception shifts into an inevitably imperfect but still immensely enjoyable version of "you are there".
So the imo the IDEAL ROLE of the in-room reflections is this: To be CARRIERS OF THE VENUE CUES on the recording, without drawing attention to their own inherent "small room signature" cues. And apparently when Matt has things dialed-in, his in-room reflections perform that "carrier" role well enough for the presentation to cross that perceptual threshold.
In my opinion.