TAMS entropy profile of a single 30 M _⊙ star (red) and engineered models where we artificially modify the CEB region (gray shaded area partially overlapping for multiple models, increasing CEB size from blue to yellow). The CEB for a single 30 M _⊙ star has a mass thickness of 5.81 M _⊙ at TAMS, while the engineered models span the range ∼3–9.4 M _⊙.