No need to question the validity of this test.
Here is a link to guidelines and an understanding of it.
https://www.cancernetwork.com/view/nccn-now-recommends-breast-cancer-index-for-predicting-benefit-from-extended-endocrine-therapy
But if you are tapering off with an expectation of the hot flashes, I just want to tell you I got a mean surprise. I have been off for 3 or 4 years and the hot flashes did not subside. It could be all about timing and all that but I will be curious to hear if it is different for you.
Have you talked to your doctor about this test, or about the hot flashes?