Uneven soundstage help, please.


I've got a pair of ATC SCM40 v2's driven by a Musical Fidelity A308 (plenty of power) and overall I'm happy with this combination, given my budget, wife, and listening habits. My system is in an incredibly complex large room, with all sorts of variables in terms of reflection, absorption, etc. And these aren't exactly the same from one speaker to another. I have no choice about speaker placement, given the room configuration.
There's a phenomenon that concerns me, though, that I haven't been able to resolve. In order to get the center centered, I need to position the speakers and listening chair in such a way that the soundstage extends all the way to one speaker, but only three-quarters of the way to the other. It doesn't sound out of whack. It's just a narrower field than I had with my older KEF References, and I wonder if it would sound even better if this was resolved.
Has anyone else faced and solved this? What factors are driving it? I've been living with it comfortably, but I wonder.
Thanks ahead of time for any replies.
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Thanks for great suggestions. More details: it's not the amp--no problem with different speakers. Equilateral distances and height and rear wall distance all the same. One rear wall is a thin layer of veneered plywood, the other is plywood backed by the metal frame of a large oven. I have one speaker toed-in more than the other, which helps vs hinders the problem That one is facing a wall of angled picture windows across a shorter distance than the other one. which faces more complex, longer angles. The high ceiling above them is slanted differentially too. I could hardly draw a room map, it's so complex.
My source(s) are the same as before when I had my old speakers-- the weak spot in my chain. But why would they suddenly worsen the moment I set up the ATCs? And I totally trust the wonderful guy I bought the speakers from. They worked impeccably in his system.
The volume from speaker to speaker is consistent. It feels like a romm/placement deal.
Of course I'll check out all the things y'all have mentioned, as well as the products/devices.
It definitely could be my ears. I'm 68 and I know I hear a bit better in one ear than the other. It didn't occur to me that this could affect soundstage. It's just something i'm used to.
I'll check connections. I did have trouble with one of the terminals on one of the speakers originally, It was very fussy.
I can't help thinking it's at least partially things about my room that are more unfriendly to the newer speakers. They're closed boxes and the KEFs were rear ported. Maybe this makes a difference? I would think it would help with a difficult room. Any more simple placement ideas? Maybe something counterintuitive?
I doubt it's the porting, but it could very well be the dispersion, or how wide speakers maintain a flat response.

In a cluttered room, you want narrow dispersion.  In a big open room you want wide.

Best,

Erik
Here's a cheap test:

Use blankets and pillows as acoustic panel proxies.  If this fixes your image, then you know what the issue is.
Erik, are you suggesting that I try narrowing the distance between my speakers or changing the toe in? I'm not sure I understand. As y'all can gather, I'm much less versed in all this than most people here.