Mobius-Silent wrote...
Ok, back home. firstly the control room->elevator-of-light->catalyst-interface-arena correspondences. (Open in new window, it's a big one)
As you can see the "Control room" is off on the rim of a cylinder segment (most of it is missing to optimise the map) This is the base of the Citadel tower (With the gravity inverted from what we're used to) the lift goes straight up to the rim of the catalyst-interface-arena. The Crucible beam runs down the length of the Citadel tower and the "processing room" teleport pads are arranged in a ring around the central shaft (which follows from the scene were we see the teleport beam start up near the beginning of "priority earth"
Side view showing Shep's path
Wow you posted that second pic as I was responding. Part of my response was suggesting that very thing you illustrated.
I originally thought the same thing you do. However, the reason I changed my mind was because of the orientation of the platform and it's ascending path.

It goes along this long narrow path. That path does not line up with the Control Room if it were to land right on top of it. The notch would actually be in the way.
Other than that I'd be ready to revise my theory because in both scenarios, the decision chamber is still from the crucible and not the citadel.