When you price a groom's cake, do you use the "wedding slice guide" or the "party slice guide"? It's really a party cake, but it's for a wedding. Some are quite simple--like a party cake, while others are more elaborate--like a wedding cake. Oh me oh my, what's a decorator to do?!
I do everything 1"x2" x height of cake to keep it consistent. At a wedding reception it's likely that the catering staff will be cutting the cake, and around here they usually cut it smaller than that anyway, so estimating party servings would be way too much cake (and too little payment for you.)
I charge absolutely everything by wedding serving pricing. It's too confusing otherwise. I don't want be asked, "Well, it's the same cake, why is it less money per larger serving for a non-wedding cake?"
Obviously...I don't sell many 8" birthday cakes, either.
Ditto as Chef Stef. I charge everything based on wedding.
I only categorize it differently. A Wedding has a minimum order of $500, a party has a minimum order of $150. (ETA - no delivery for party cakes either)
It's never an issue when you have the same price for all cakes.