I figure my number of servings based on a 1"x2"x4" per slice.

How do I determine the number of servings if the tiers are not 4"? For instance, if some of the tiers are 3" or even 6"?

I have used the Cakulator to determine # of servings, but it won't let me say that I want an 8 cubic inch slice. It just keeps the same number of servings with a larger volume of cake.

http://shinymetalobjects.net/cake/calculator/cakulator.html  

How do you account for the difference in height?

Here's a picture of the cake that makes me ask this question.