Read the opening stage, not size alone
A firm bud, a flower beginning to open and a fully open peony look different and continue changing after handover. Several stages occur naturally in one living batch, so the bouquet should not be expected to contain perfectly identical flower heads.
Compare the photograph, stem count and full product dimensions. Large open blooms create volume quickly, but the actual scale also depends on variety, foliage, wrapping and any other materials in the arrangement.
