how specific do the scenarios need to be to get a good branch

New to this one. The example in the card does the blue-pill/red-pill Matrix scene, and I tried something similar with a random historical moment but the answer came back pretty vague, more like a summary than an actual alternate scene playing out. Do I need to set up more context first, like naming the exact moment and who's there, or is the vagueness just how it handles anything that's not already a famous well-documented scene?