Let me see if I can describe my L/C/R setup here:
My speakers sit up near my screen on either side (floorstanding) and my centre is on a small table. They are 8-10" from the wall.

The key here is that they sit in an alcove (where my screen is) that is about 2 1/2' deep along the walls (my entire 106" screen with room for the speaker son either side also sit in this alcove; the remainder of the room looks into this alcove as the front of the dedicated HT room...man I wish I had a picture). The alcove about 1' from the rest of the ceiling (again, 2 1/2' deep).
The front of the floorstanders are just inside the alcove area, and the centre is deeper in. This alcove is 12' wide and about 6 feet high. The rest of the room is 7' high outside of the alcove area.

My questions are:

Would I get better sound moving them slightly out of this alcove (and thus more towards the audience?) This would also help establishing more of an even triangle of distance between the L/R speakers and the listener's seating position).

However, it would also move the front of the speakers (including the centre) about 2 1/2' to 3' from the screen, which could lead to a dislocation sound. Is it important to keep the speakers as even as possible with the screen?

What should I do?

You should keep the center channel as close to the visual display as possible, and the L/R speakers should be 1 to 1.5 times the distance away from you as they are from each other. IE If your speakers are 5' apart you should be somewhere around 5 to 7.5 feet away from them, diagonally.

For distance from rear wall, I start with a very basic method. Stand with your back against the rear wall, and while talking walk forward slowly. You will notice a resonance in your voice disappear suddenly. This is the starting point to place the front baffle of your speaker. The same from the side walls...

If your more into math, you can find many calculators out there that describe the best position based upon your room dimension. I've listened to setups based upon these calculations and they work, if you want directly radiated sounds to reach you before first reflections, probably the best way to judge speaker quality, but maybe not for listening pleasure....it's pretty subjective.

But all in all, use your own ears. If you like what you hear, don't change a thing. But if you're into tweaking, be prepared to spend LOTS of money and/or time to gain that extra 10%.

Thanks.

So can the center be let's say 1 1/2' farther away than the mains? ( in order to keep the centre close to the screen, but the mains out of the "niche" I have? They resonate a bit in that niche.

Most receivers have this adjustment, usually in feet from listener, some in actual delay in milleseconds. So yes...it can be done.

Most receivers have this adjustment, usually in feet from listener, some in actual delay in milleseconds. So yes...it can be done.

Yes, mine has it as well. But I was wondering if it was a best practice to do it? I guess it's whatever sounds good eh?

I had once thought that the centre and mains should all be equi-distant from the listener. Guess not.

In a perfect world they all would be, but unless you build a room for your theater, it won't be.

In a perfect world they all would be, but unless you build a room for your theater, it won't be.

That's the thing, I do have a room I've built for my theater, this is it. And this is my problem (i.e. described in my op).