AWhen doing an anniversary (tier) cake, do you charge based on wedding cake slices or party slices?

Any tiered cake should be priced on wedding slices.   In fact, it really doesn't have to be a tiered cake.  If it is 4" (or more) tall, then it is served 1"x2"x4" - wedding slices.   If the customer wants to serve bigger slices, then they need to order (and pay!) for a larger cake. 

Say the customer want to serve 57 people *large* pieces - then they order a  cake that serves say 70 wedding servings. 

I had a customer who only wanted to serve something like 10 or 12 people but they were BIG! cake eaters so she ordered a 12"x4" round :)  If I remember right that serves something like 54 wedding servings.

AThank you so much.