Google Music does it the same way: https://play.google.com/intl/ALL_ALL/about/artist-terms.html

""" (a) “Subscription Fees” shall be the greater of:

(A): Monthly Subscription Minimum * number of Google Play music subscription service subscribers on the last day of such month * Your Subscription Activity Ratio

-- OR --

(B): Subscription Revenue Share * Music Subscription Revenue * Your Subscription Activity Ratio """

B is exactly what is laid out in the parent article, A is a subtle twist on it. Both of them are still [Google's revenue] * Your Subscription Activity Ratio, where "Your Subscription Activity Ratio" == "the fraction: (i) the numerator of which shall be the total number of streams and plays of Your Tracks from the Google Play music subscription service; and (ii) the denominator of which will be the total number of streams and plays of all tracks from the Google Play music subscription service."