Well, I guess you mean the first paragraphs? Because a scene could be a mixture of all the throughlines, couldn't it? Even a sentence fragment, sentence, or paragraph might perform double or triple duty. As I mentioned before, I've become obsessed with first paragraphs. Here's my first draft first paragraph from my current project:
Bonaventure Faust was forty-something years of chancy living and fickle luck being worn by a double-breasted grey suit. A matching fedora was propped on his face. He was sleeping last night off in a torture device shaped like an office chair and his dogs were lounging on the back left corner of an oversized footrest called a desk. A metal flask rested on his paunch and under his hands like a beloved teddy bear.
This starts in omniscient POV. The last sentence slides into the MC's POV. But, I'd say that the first paragraph is primarily within the MCT as the reverberations of the Inciting Event don't affect my MC until 8 scenes later. I still think that certain concepts might be hinted at in regards to the OST.
This is the type of question that I enjoy. I guess part of it depends on how you define beginnings. First sentence? Paragraph? Scene?
My first scene is definitely dominated by the MCT, but couldn't OST or RST or IC concepts be hinted at with foreshadowing or narrative tone, etc?