For anyone wondering (as I was), Kindle Unlimited pays per page based on the size of the fund (number of subscribers total), and the number pf pages read during that month.

>Here are some examples of how it would work if the fund was $10M and 100,000,000 total pages were read in the month:

    The author of a 100 page book that was borrowed and read completely 100 times would earn $1,000 ($10 million multiplied by 10,000 pages for this author divided by 100,000,000 total pages).
    The author of a 200 page book that was borrowed and read completely 100 times would earn $2,000 ($10 million multiplied by 20,000 pages for this author divided by 100,000,000 total pages).
    The author of a 200 page book that was borrowed 100 times but only read halfway through on average would earn $1,000 ($10 million multiplied by 10,000 pages for this author divided by 100,000,000 total pages).