That's a good estimate for an individual visit as of today but is precisely the kind of thing that which has resulted in "normal" tips going from +.1 to +.15 to +.2 as the years go on (erring too low has more friction than erring too high, and if something else raises the amount traditionally tipped somewhere then "normal" for this will tend to adjust upwards in a large group).

Will owners realize at some point that the tips are really coming out of their pockets? If a guest has to pay $10 tip, she will buy $10 less food.