You can't get a "verified customer review" if somebody reads your book through Kindle Unlimited. And if a review is not verifiable, it has less importance. So, we're sticking to the important reviews. Besides, if you price your eBook low enough to entice Medium readers to buy and review it, they will. You will get a sale out of it as well as a review. And this will increase your standings in those Amazon statistics. My book, which I've listed, is priced at $2.99. This seems to be best for garnering reviews and sales. I'm going to have to write something like this in the publication, I think, to answer questions like yours.