Micro position adjustments

Everything matters.  IF you can hear a difference, that is.
When you can hear a difference, then it makes a difference.

Do you notice a change in sound after vacuuming the carpet?
Changing the humidity in the room?
Adding/removing lighting devices?  Having them on or off?
Wiping down the walls (anti-static fluid)?

You may want to read Jim Smith's "Get Better Sound."
He maintains there should be nothing between the speakers...

I’ve always suspected.....and assumed humidity would affect speakers especially (anyone with a guitar knows how their neck changes and expands in summer humidity vs. winter dry air)....enclosures and drivers would change mass etc.
Hard to get a grip on that though since it happens over weeks/months.......

Change after vacuuming the carpet...😮😮😮🤣🤣......you’re probably right, anything is possible!

toe in and out is critical. finding the best room balance location is critical. most speaker manufacturers have recommendations based on the speaker design as to the ideal approach relative to the listening position.

but once you think you are close; try laser aiming and leveling. we call it ’stereo’ since it’s 2 speakers providing one soundstage. the balance of these two speakers determines the precision and tonal balance you hear.

the taller your speakers are the more this matters as the drivers are then more prone to be out of alignment. i have twin 7 foot tall towers where this process is critical for optimization.

there are devices you can purchase that can be attached to the face of a speaker that will allow you to exactly aim the speaker. also to level the speaker sitting on top. it’s spins around indicating the top is level.

you get a tripod with a piece of paper with a crosshair at the spot for your ears. once the speakers are known to be located at the exact same distance then the trick is precise aiming.

of course; it helps to also center your speakers exactly if your room is symmetric. i have a symmetric room with a piece of tape on my hardwood floor precisely measured down the center line which helps to measure the speaker position, but also when i’m listening it allows me to ’sight’ down the center for critical listening times.

you spend all this money on gear, and spend lots of time listening. this last little effort does pay constant dividends in what you hear.

wall. ceiling and floor treatments are a whole separate question. but every stereo system benefits from perfect alignment.

I’m one who doesn’t believe equipment should be in between the speakers as it will negatively effect the soundstage and overall performance of the speakers. So it does not surprise me that moving equipment between the speakers has an effect. My rack is to the side. 

On the other hand, yes, even small adjustment to the speakers themselves can can substantial changes; width, dimension from the front wall, toe-in, etc. without equipment between.