I finished the installation of wider hinges to let the seat back on my Axis couch tilt back further. It worked pretty well.
The back rest angle is determined by two hinges that attach the seat back to the couch's bottom structure. As it comes originally the seat back actually tilts forward a few degrees. It would be much more comfortable if it tilted back about 5 degrees. There is about 6" of room behind it to let it tilt back further.
See the pics below. The first is one of the OEM hinges (left) along side my modified hinge. I used a couple of hinges that I had hanging around which required filing the holes oblong to make them fit, but check at your local hardware store, you may find some that work as is.
Note that the distance between the elongated holes on the right is about 3/4" more than the left ones. That was enough to let the couch tilt back another 2" as seen in the before and after pics.
It isn't perfect but it makes a miserable couch into an acceptable one for me by allowing the seat back to tilt further aft.