Looks good! IIRC, the pink is about 20kg/m^3 while the blue Dow styrofoam is 32kg/m^3. Look it up though, I'm not totally sure about that! Denser is better. As far as I've gathered from reading, the blue one is reflective down to about 4-500 Hz, while also giving some absorption down to about 150-200Hz. Good enough reflective properties for the application at hand, with the added low mid absorption as a bonus.
The build looks good. Using well dividers will make it quite a lot more effective. As it is now, the diffuser will only provide for the number theoretical performance for waves that hit the array in a perpendicular direction. Grazing angles will see an irrregular surface and something is still going to happen, but it won't give the nice spread in the energy that it could do with well dividers.
Lastly; invert the direction of the end cuts! Where there's a small bump going up above the surface of the well. Having it pointing inwards will be fine, as it is now, it's breaking up the pattern.
PS: in case you haven't noticed, there's a thread about the 2D diffusors I make out of styrofoam.
