It would seem that they would need the array to get sufficient resolution to make sure the light wasn't coming from anything other than the accretion disk of the object in question. (Ie: using the resolving power to improve pointing accuracy). The extra gain would also be handy.
Looks to me, like they're creating interference patterns to measure the phase differences in different parts of the image. This holographic plate must enable them to establish the interference pattern (a bit like a diffraction grating ... in 3D)
Interesting, none-the-less.
I wonder how they differentiate between different objects having different grav. fields ? I mean, it would also work for other objects like a neutron star wouldn't it ? I guess the more the intense the phase shift pattern is, the more intense the grav field of the object. I also guess the calibration of the model involves a lot of theoretical calculations ..
Cheers