The structure of the CEB at the end of the main sequence impacts the envelope binding energy profile throughout the remaining evolution. Dashed lines show the gravitational contribution only; while solid lines include the contribution of the internal energy. The red lines show a 30 M _⊙, nonrotating, Z = 0.0019 model compared to “engineered” models of the same mass (see Figure 5, increasing CEB size from blue to yellow), but artificially imposed profile at TAMS (other colors; see text). The top (bottom) axis indicates mass coordinate (radius). We compare the models when they first reach 500 R _⊙.