The distance between the loudspeaker and the treatment is not relevant to any consideration I've ever heard of - assuming the treatment isn't in front or something, obviously.
The distances that matter are the distance from the speaker to the natural boundary (wall, etc.) and the thickness of the treatment. The distance between the speaker and the wall determines (basically) the frequency of the null created by the interference of the reflected sound. The thickness of the treatment should be adequate to absorb as much of the sound energy at that frequency as possible. Without doing all the math, and making a judgement call based on my own inexperience, I think you're okay.
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.