I forget what SBIR really stands for but it's when you place a speaker too close to the side wall. SBIR isn't really an effect of the wall behind the speaker. Essentially, if you place your left/right speaker too close to the side wall it creates a pressure wave that "loads the wall" and creates a blare or increase in sound pressure. The resolution is either to move the speaker away from the side wall or place a sound absorption panel on the side wall right next to the speaker (or maybe just slightly in front of the speaker).
Putting sound panel on the front wall behind the speakers is to treat reflections. The sound will travel out from the speaker and hit the back wall which are reflected back towards the speaker itself and then reflected again on the wall directly behind the speaker. You do not want this. This is why panels are often placed behind the speakers, but it's not technically "SBIR".