Lack of depth problem

congratulaiton !!Nice to learn that you 've overcome your
speakers problem.

Since you have a spacious room, 15W x 23D
Previously your problem may be the wrong ratio used :-
5 ft Vs 18 ft ( rear / front )
or 5 Vs 23 ( rear / total )

Now 9 Vs 14 = 0.642 ( +/- other room furniture/book shelves
etc , cannot make the exact clcualtion herewith )
The more closer to 0.618 the more it becomes improved.

The H Vs Rear 1.0 is of no bad-effect .

Best reuslt can be implemented by standing Panels ( which
I am using ) if the room cannot cope with such ratio's.

I think you will find that you would see a better result by aligning the speakers along the length rather than the width of the room if you can do that, because 2.5 ft from the side walls sounds awfully close to me. In my experience soundstage is dramatically affected by side wall reflections. I have Virgo 111s set up along the length of my room, about 7 ft out from the sidewalls, with amazing soundstage. Hope that helps.

I second opinion of Robert1897

Speakers along the longer wall will definitely increase
the clarity whilst the other way will be with increased
low's. But increasing the degree of toe-in will help to
reduce the low's.

Depth is improved and more felt with a deep soundstage
as it is against the 15ft shorter side.
Judge with your own ears / preference.
as well as you have so many vibration-absorbing objects
in the room, actual hearing is the only way.

If you are approx 10 ft from speakers, try the " longer Triangle method ; try them as 8 ft apart ( less toe-in than
10 ft apart ) it may also sound good.

Yes, 2.5ft is indeed very close to the side walls. I had boomy bass first. Then I put a bass trap panel along the long side of the wall next to one speaker. The bass is clean now.

Regarding Mezzo vs. Alto Utopia, I think JMlab upgraded the tweeters to BE tweeters. The highs are mega powerful!

The only problem I see in my setup is that my rear wall should have been more reflective. Then I will get a more spacious sound stage.

Roberts, how far away are your speakers to the rear wall and to you?

My speakers are out about 4 ft from the rear wall. I have my speakers on spike pads that allows me to slide them out into position when I'm listening to them and slide them back out of the way when I'm not. Very handy, as otherwise they would be stuck in the middle of the room.
I recommend you to go to the Audio Physic website. It gives you a very comprehensive guide to speaker setup that is applicable to all speakers. Their approach makes a lot of sense from an acoustic perspective.