what kills soundstage depth?

Easy - now you have posted photos - the speakers are too far apart. If you want
depth then get them closer together - the way you have them is too much like
headphones (think headphones put the depth flat - sounds in your head). Each
ear must be able to hear BOTH speakers directly (and the funny flab of skin
around your ear plays a big role here and performs best with sounds from in
front rather than to the side)

Jimmy,

The equilateral triangle is most useful for mixing or mastering. If you want a more 'realistic' presentation then I prefer speakers facing forward (not toed in) and about 2 feet apart for 3 foot listening, 4 feet apart for 6 foot back listening, and 8 feet apart for 12 foot back listening. The further back the more natural and less like headphones it will sound - however you need correspondingly bigger space as you need at least 6 feet open space behind the listener and if you place speakers 8 feet apart then you need a room that is at least 16 feet wide.

Whatever you do DO NOT sit with your head or couch up against a wall - this is the single worst thing you can do in any listening room - if you cannot hear the damage done to audio from sitting at a wall then you probably need not waste money on audio gear. I see that you have a seat closer to the middle of he room than your couch - I assume you hear the degradation from sitting at the couch and use this seat for critical listening?

A dipole type radiation pattern will increase your sensation of depth due to midrange energy being reflected off the back wall.