Generally speaking, when it comes to effects shots in Super 35, these are done in roughly a 2:1 AR, since to do the effects in the full Super 35 frame isn't cost efficient. 2:1 gives some leeway in a 1.33:1 transfer, but not much.
The LOTR films are shot in Super 35, which is why it is relatively easy to generate a 1.85:1 version or a 1.33:1 version. It's a concession Jackson made to New Line, since the budget for the three films is the most NL has ever spent on a single project.
I was just watching the extras on my T2:Ultimate Edition last night, which include a rather elaborate explanation not omly of the formatting of Super 35 to video, but also of the creation of a widescreen anamorphic print from the Super 35 negative, and Cameron once again used the same qualifiers...