Originally Posted by DeniseNH
Okay, but thinking about it another way. Both pans use the same amount of batter. The round pans cake will bake up slightly taller than the square pan cake. Let me put it another way. The little bit that fills in the corners in a square cake makes the same size round cake taller, but it's still the same amount of batter. The hall can cut slightly slimmer slices of the round cake and slightly wider slices of the square. Volume remains the same but perception of a difference persists in articles published by authors not associated with the wedding industry.
But the OP already noted their tiers are the same height--so the volume is not the same. Therefore the hall would not cut the slices any differently.
You seem to assume that squares will not be as high as rounds. However there is no reason to assume the same amount of batter would be used in both (keep in mind the OP claimed the tiers are the same height) Serving charts make no such assumption.
First the standard chart for servings (or at least one of them) notes that it takes more batter to produce the same sized square. Second it notes that based on the standard 1x2 serving no squares will produce more servings than rounds. Thus it is not authors not associated with the wedding industry that are publishing articles producing a difference that does not exist. A difference does exist.
There is simply no reason so expect a difference in height simply because a tier is a square instead of a round. The same amount of batter should not be used in each. The batter for a round does not determine how much batter should be used in another shape (square, heart, oval) of the same size.