This is what Stuart (Soundman2020) at the John Sayers forum had to say. He attached a picture of the lobing but the link isn't working.
QRD diffusers (a.k.a. "skyline" diffusers) are based on numeric sequences. Your room is too small to be able to use numeric-based diffusers. They can only be used in larger rooms. All numeric based diffusers produce temporal lobing, frequency lobing, and lelvel lobing, close up. What that means is that they create patterns of sound waves that are more intense in some directions, and less intense in other directions that are only slightly different. As you move around in front of them, close up, you get areas where the timing (phase), intensity (volume), and frequency are not scattered evenly. There's a certain distance that you need be away from the face of the diffuser in order to hear a smoothly diffuse sound field, once the irregular patterns have evened out better. That distance is at least ten feet, regardless of the diffuser tuning, and can be greater than ten feet if the diffuser is tuned low. Yours is. Your room is too small to be able to get your head far enough away from the diffuser, and the poor guy sitting on the client couch is toast! He can never get any kind of diffuse field, since his ears are just inches from the diffuser.