The difference between what you describe and what I describe, is that a 100% match isn’t a hit. Nor is a 90/7/2/1. You need something with meaningful variability. Even within formal papers there are places where word choice is arbitrary as the article explains.

Of course, you’re lacking the context of the full prompt and just feeding in the raw text. Again it gets way more reliable the more text you have.

But it’s moot because the more text you have the more tells will sneak in and you probably don’t even need an AI checker. Those phrases that AI loves but humans use comparatively rarely. It’s not a tell — it’s the whole game!