Aborbers proximity to walls and speaker

How close can you have an absorber to your speakers
My room is quite narrow by placing an absorber on the side walls to treat first reflection there isn't much room between speaker and wall does this effect impact

I was told due to the loading of the room I should be using a 4 inch panel instead of a 2 inch one but that won't give me any room
See pic of my system in the virtual page