Question on Speaker Placement

The back wall is important because sound will bounce off the wall back to the listener. You want symmetry in your room because now,  1 of your speakers will get reinforcement from the back wall and the other speaker won’t. If it’s for casual listening who cares but in a more critical listening environment, you want both speakers the same distance from the back wall, the side walls, and from the listener position.

Thanks for all the feedback and suggestions. One common question, and rightly so, was "Do you like the sound? or "How does it sound to you?" I've been generally pleased with the sound in the room as is, but like many concerned citizens, I'm always seeking improvement, the cheaper,  the better. Keep them cards and letters coming!

The only thing that matters is how it sounds to you.  From your description you will likely get more lower frequency SPL from the speaker in front of the wall while the speaker that is floating won't be able to match the others SPL.  The only way to really discover what they're doing is measure the speaker's responses.  The free REW software is a great tool to sort out difficult rooms.  Keep in mind that when speakers get more than 9ft apart it gets more and more difficult to get good imaging.  Good luck and cheers. 

Many years ago John Rutan at Audio Connections in Verona, NJ had a listening room configured with the speakers along a diagonal of the room, rather than parallel to a wall. It sounded great with all the speakers I heard, probably four pair. For the past couple of years, I’ve finally had a room that’s amenable to such a setup, and it works out really well. Now, I’m using dipole speakers, but none of the speakers John played for me were dipoles, and they all sounded good in that configuration, so it’s probably worth a try if you have an appropriate room. And using a real time analyzer app, I seem to be getting pretty flat response, although I can’t compare it to the response in prior rooms with parallel configurations because I only discovered app after moving to my present house. 

Find a track you really  like that has full dynamic range. Place tape on the floor where your speakers are.

Move them all around, each time listen to that song. Place tape where you think things work, repeat till you find the "sweet spot"

When you figure out what sounds best, leave the speakers there.