that is not a QRD, so i am not sure why it is labeled so. it's actually an old BBC design composed of many smaller PRDs into an array; hence why the wells are 12x12 and thus do not correspond to a single primitive root diffuser (12x12 are not co-primes). a PRD based on P157 would yield 13x12 wells (13x12 = (157-1)), for example.
diffusers (phase gratings, in this case), break-up sparse reflections into many reflections spatially and temporally dispersed (grating lobes). a 2D diffuser (your example), disperses energy in the vertical and horizontal planes, while a 1dimensional phase grating will disperse in the opposing plane of the wells (eg, a 1dimensional diffuser oriented such that the wells are vertical yields spatial dispersion in the horizontal plane).
you first need to understand the requirements of your room and how you want to introduce indirect specular returns to the listening position. for a 2ch environment (if emulating the LEDE response), you would utilize 1dimensional phase gratings on the rear wall/side walls with the wells oriented vertically to provide a lateral-arriving
diffuse-field for passive envelopment. a surround sound environment has active surround sources, so a 2D may be more appropriate since the passive lateral returns are not needed. a 2D will also have an inherently higher absorption coefficient due to the increase in number of wells (1/4wave reson and edge diffraction losses), on top of the additional losses due to redirecting energy in both planes. regardless, care needs to be taken with respect to construction to seal any/all gaps to eliminate excessive losses.
you will want to be in the far-field of the diffuse returns, and as such it is best guideline to have listening position be at least 3x wavelength of the design freq away from the diffuser. eg, if your listening setup is ~ 7ft from the diffuser, then you would utilize a design freq of 500hz (corresponding to 2.26ft wavelength; 3*2.26 = ~6.8ft). this requirement can pose issues in smaller rooms with many seats and as such you will commonly see Binary Amplitude Diffusers (BAD) utilized, but these devices will only offer spatial dispersion (no temporal dispersion).
instead of blindly following a diffuser template, it is best to utilize a QR or PR
calculator in order to design the diffuser based on your criteria: minimum seating distance to diffuser (=design frequency), sq area / array size you need to cover, complexity of construction, prime#, etc.
a 2D primitive root calculator can be found here: http://www.oliverprime.com/prd/?show=gallery
a 1D/2D quadratic residue calc can be found here: http://www.subwoofer-builder.com/qrdude.htm
QRDude is a wonderfully written app and you should take some time to read through the technical guide of which will detail the physical aspects of the behavior: http://www.subwoofer-builder.com/qrd.htm