Its really based on whats in your heart, and how you felt about there extra service. If you feel $10.00,or $20.00 is enough, so be it.
On our last cruise,we tipped our bar attendant and her helper an extra $20.00, our room stewardess an extra $20.00.All this was extra, we did leave our prepaid tipping on our s&s card.
Just listen to your heart
Happy sailing and smooth seas;