You need to balance peak heating and heating duration. Shallower reentry means lower peak heating, but higher heating duration. Steeper entry means higher peak heating, but lower heating duration.
The heat shield material can handle a certain amount of heat and a certain maximum temperature before it starts to ablate away, so you're forced to thread the regime where both variables are within its tolerances.
The heat shield material can handle a certain amount of heat and a certain maximum temperature before it starts to ablate away, so you're forced to thread the regime where both variables are within its tolerances.