Fang Zei said:

But for a scope movie like Star Wars, it really should be the full 2048 that's being used. 2K for scope is 2048:853, 2K for 1.85:1 is 1998:1080 and for 16:9 it's, of course, 1920:1080.

Yes---although commercial 2K cinema projectors can scale/stretch up the image in the vertical direction(thereby utilizing the full 1080 x 2048 panel)

And with the help of an anamorphic lens---optically expand the image horizontally.

For those who own projectors which have this same scalability function---It can also be done at home (but consumer anamorphic lens cost somewhere in the region of $5000-$10000).

P.S

I have a Sony 4K 1000es projector and have watched Eps IV,V and VI at a resolution of 1706 X 4096.

The below screenshot is from projectorreviews.com:

They scale up perfectly and look nothing short of amazing.

Same applies to the prequels with Revenge Of Sith being the standout.

This screenshot below is from an AVS forum member :