This cannot be right, how can this makes sense with mobile gaming? Unity has a HUGE market share there, so they know the number. How can free games ensure a 0.20$ per install? Why not go with X% of the revenue?
Unreal isn't being used to crank out low end mobile games that are purely ad sponsored... betting that there are more shenanagians going on in unity's space that would means it hard to actually check the books versus someone with 1M in revenue