I assume you are testing for Cushing's. The ranges are not accurate as the dex test is a separate test. 1.2 is considered a fail, 1.8 is the cutoff.
However, I can tell you from my experience and from many others that I failed this test (badly) and I had Cushing's. It is a better test of location rather than exclusion, but a doctor inexperienced in diagnosing Cushing's will run this test first and say you are fine.
I don't have any other details, but I would find another doctor.