Are you sure you're talking about forward projection, not depth? I feel that forward projection has a lot to do with how vocals are placed in the mix.
Edit: just for illustration, in my understanding forward projection is independent from actual soundstage dimensions width/depth/height:
I was positive when I said forward projection.
Forward projection is independent from stage size as far as I'm concerned, but a stage of equal dimensions will feel larger regardless if projected forward because the listener will associate that gap between them and the stage as part of the stage, what some might call the 12 rows in front of them, and add it to the dimensions.
The 1plus2 does something a bit different and because you've inspired me to go back to my 1p2 EQ Project, I think I may have hit upon a few things today.
Mainly, that I both agree and disagree with you. Here's my diagram:
The area within the orange space is the stage. The pink boxes are the general positions of most images on the 1p2.
What it does uniquely is instead of just projecting the whole stage up, it creates a sort of faux void right in that center area in front of the listener where mainly bass sits atop, having that more omnidirectional quality.
What I didn't realize when i was playing around with this long ago, is how deep the dips at 3k and 6k on the 1p2 are. It's not just the midrange that we see on the measurements scooped out before 2k that does it. Everything above 2k is critical.
IMO, the trick is that it pulls important sections of the FR back and allows the bass and areas where a lot if harmonics reside get emphasis. This way we get that forward projection, but then we also get the harmonics flying up at is because of the treble peaks, giving the illusion of distance of the midrange.
I couldn't get enough distance in my EQ until just now when I pulled 3k and 6k waaaay back like 700Hz.
Then having the images that only hit mainly one side waaaay up front near the ear adds to this illusion.
And the treble peaks create that more oblong stage shape nearer the listener, pulling it in and up toward having more height.
The tuning of the 1p2 is brilliant to me, with absolute purpose.
Obviously there is more to it with other factors leading to a good starting point (what those are I do not know), but the FR is a marvel of ingenuity to go with whatever magic Gavin's team concocted.
When you get the Rockets, I'll send you the EQ so you can see what I mean.
I'd actually love for
Joe Bloggs to take a crack at it