I don't think the dish is being "installed" as much as repositioned or configured. It could just be in the middle of positioning for maintenance, calibration or aiming. Moreover, I would imagine that being able to remove or at least create a space to work behind it would be important to its development.
But here's a little more context around the dish's use and capabilities from Catalyst:
The plan, in any case, called for assembling the dish in space and maneuvering it by tug and tractor beam into the gargantuan well that had been framed into the sphere’s upper hemisphere—the dimple, as some referred to it. The parabolic dish also had to be engineered to telescope away from the hull to facilitate the aiming of the composite beam proton superlaser some of the Special Weapons scientists were proposing.
So really, the fact that the dish was "popped out" at the time of the scene might have nothing to do with it being "under construction" at all. And I think the image from Revenge is the "gargantuan well" that this is referring to.