What affects front to back depth in room/ system?

This has a lot to do with equipment quality and system setup

You need high resolution gear and a system setup with good cabling power vibration conditioner vibration reduction you haveto maximize what the system can show you and if it is in the recording you should get it

Acoustic treatment in dimension of concern.  Diffusion behind speakers and listeners, ceiling absorbers between speaker and listener

A primary factor is how much space behind the speakers.

My current setup, wall behind, I get great imaging EXCEPT limited Depth

Prior Location, Long Space, Speakers 2/3’s out facing Living Area One End, Very Wide Archway Open to Dining Area Behind Speakers: MORE DEPTH.

However, the reverse existed regarding rear wall reflection timing..

Prior: Sofa against rear wall, quick rear wall reflections

Current: Open space Behind Listening Position, diminished volume of and increased time delay of rear reflections, improves precision of imaging.

And: Rear PORTS: Closed here, Open Prior (a bit of extended bass out of the 15" woofers) too close to rear wall now.

I was young, thinking too much, had Electrovoice Engineers help me with port design, never needed, waste of time.

My friend has my old JSE Model II’s, he loved them here when younger. He lives in a Firehouse he bought, they have PLENTY of space behind and to the side, he updated the crossovers, changed the tweeters from those nice but easily blown Dynaudio D21’s.

HOWEVER, like my prior location, his sofa is against the wall behind. I keep telling him, treat the wall behind, minimize the rear reflections. He mentioned he has a giant American Flag. I would glue a thick layer of old fashioned carpet underlayment on the wall behind the flag.

He thinks he may reverse everything in the big room, then he would have plenty space on sides, rear, and behind his listening position, that ought to be better than ever.

Maybe when setup, I’ll have him and a strong friend or two move my current speakers over there, hear them in that ’open’ setup for the first time, and he wants to compare these to the Model II’s.

If I understand your question, you are looking for something very unusual. Typically we look for the soundstage to begin at or behind the speakers… like at a concert. The stage, is where the sound comes from. The mark of a great system, in part, is it being laid back with a deep / wide sound stage.

Some speakers can be “forward” typically having a shallow sound stage… typically this is a criticism of the system because it is not reproducing natural sound.

There is a few home audio speaker systems that are are designed not so much to do the sound-staging.. but to produce a wall of sound. The ones I remember hearing were six or seven feet high, with tweeters in the middle and mid range above and below then further out woofers above and below. I don’t remember names.

i would recommend trying your system against the short wall. Making sure there is nothing taller than an amp on the floor… equipment racks typically interfere with sound staging.

It would be really helpful to see your system in its current form. There is a place for photos along with your equipment.

@veerossi 

Most importantly, set speakers on the 15' wall, not the 20' one. Then place them at least 4' to 5' from front wall and 2' to 3' from sidewalls. Only then will you start getting the full 3D effect. By my experience anyway.