I suspect that if the rate was $4. pd ..pp for the waiter on a 10 day it would be $40. so if you gave him $100. he would turn in the $40. and keep the rest.
Just my guess though ...you might ask on the crew forum how it works
You could just leave the auto tip on your SS card then tip what ever you want to a specific person then he keeps it.
I am not sure how it works out but I have heard if they don't turn over the tips they can be dismissed.