Time of day is a factor too. Some more budget minded hosts will hold an event at mealtime and say canapés only. In that case we provide more because if not it looks like we were unprepared. Also if anything is tabled instead of passed and you provide plates instead of napkins people will eat more. Straight up cocktails from say 5-630 with everything passed we do 4 or 5 pieces per person. If it is tabled guests can sit and we are putting out ap plates we double that. It's amazing what a guest can fit on an ap plate when they think its a dinner buffet.