Your friends have higher VIP rank than yours, right? Perhaps, Stake hasn't given the bonus by considering the recent wagering amount. Maybe it was a fixed bonus amount based on VIP rank. Although fully inactive user might received lower amount than they should (for their VIP rank). I think Stake has given the base amount to those players who have recent game play activity. So huge and small wager hasn't made difference in the bonus amount. The VIP level did everything.