simple calculation:
pay 20 eur to an user that generated 40 eur, the user will generate another 40 eur, profit: 20 eur, from profit pay 1 other 20 eur user
pay 300 eur to an user that generated 600 eur, they will generate another 600 eur, profit 300 eur, from profit pay 15 other 20 eur...