The distinction
A sentence can be easy to read and still be wrong. Ease is not a source.
Fluency is the feeling that a line is finished. Evidence is a claim you could fail. An artificial answer is built for the first. It is not built for the second. That is why your artificial SI sounds sure: the costume is the product.
Keep the draft if a step in it is specific. Drop the trust if the only thing it gave you was relief. The longer version is why it sounds sure.
Then check the signal