There's a catch 22 here though. If the company does well, the new hire equity amount will drop because the stock is more valuable, and thus the evergreen grant will pale in comparison to the employee's earlier grants. Should the evergreen grant be relative to the original grant?
If the company is doing poorly, people are going to look around regardless of equity.
Investors and employees make much more money by increasing the size of the pie rather than their share of the pie.
Percentage-wise the new grants will be smaller but could theoretically match the (estimated) dollar value of the original grant, if they are considered based on the time each was granted. Obviously, the new hire grant will be worth much more than the evergreen grant at the time the evergreen grant is given. But the employee is now taking much less risk than they did when they joined, which is covered here:
The best part is that, as your company grows, you always grant stock in proportion to what is fair today rather than in proportion to their original grant.
If the company is doing poorly, people are going to look around regardless of equity.