Album split, but no "compilation" option in iTunes 12?

Hi!

Okay, I'm one of those neurotic people that want all of their music to be all organized and stuff.

Today I bought a four-disc box set and loaded the discs into iTunes, correcting the information and sorting fields as I usually do so that they all fall into one clean album. However, after all that work (and successfully getting the entire collection to sort as a single album in iTunes), when I loaded them into my iPhone the album was split - three discs in one "album," one disc in its own "album." Kind of annoying, but oddly specific enough that it seemed a fix was easy to find.

I did some digging in Finder and noticed that those three discs are sorted in Music > Compilations, and the fourth disc is sorted in Music > Various Artists, which also coincides with how my iPhone is sorting them. I tried everything, but that fourth disc will not settle into a "various artists" compilation on its own like the first three discs. Unless I force it to sort as "Various Artists," it will split into five albums for each artist on the disc. Now, back in the days of setting the entire album's "Compilations" tab to "Yes," this would be fixed in an instant. BUT NO. The compilations tab is NOWHERE TO BE FOUND.

Am I missing it? What can I do if that option is no longer available?