room set up question?

Typically there is only one sweet spot and by the nature of most speakers… that is it. There is variability… planar sweet spots can be tiny and require speaker placement to be perfectly adjusted to the 1/8”… or smaller. Most speakers will have a sweet spot of a foot or more wide. You usually optimize for the center of a couch and sit there when alone and in music appreciation mode. When joined by others the sound will be good… but the sweet spot is where it is. It is three dimensional… with similar heights, widths and depths. Moving your couch back will only suboptimal all seating position.

I have a love seat with the sweet spot in the left position, leaving the right position open for one or both of my dogs. One in particular loves music and joins me regularly, but has not tried to claim the sweet spot as her own.

There are also Omnidirectional speakers that attempt to open the sweet spot up. Walsh and MBL are two such companies. I personally cannot recommend Walsh (I did own some a long time ago)… but some folks like them. MBL Audio Radialstrahler’s would be a fantastic choice but are fairly expensive. 
 

Try experimenting with tow in, start with none and then see how aiming toward the MLP changes.

To get a really nice result try using room treatments.

Watch this video with headphones and see how these diffusors can enhance the sound. The panel setup in the video will probably work for your room too: