I recognize not everyone agrees with this approach but it always has worked well in my experience.

I am a strong believer that refresh grants should not be given only to "high performers".... I believe in using a consistent model for all employees, (the Wealthfront approach always the simplest and best in my mind) under the conception that you'd give the same amount of equity to a new hire in the role and you want to always keep your employees evergreen and future looking when it comes to vesting.

If you don't think an employee is performing well enough to deserve more equity they probably shouldn't be working for you in the first place, and on the same side they can always get a new grant in a new role if they can't with you. So I've found it a healthy way to drive retention.

Separately, I've always given separate additional performance equity grants to the stars that are really having an outsize impact and outperforming their role.  That's over and above what they'd normally get through their regular grant, and comes with accelerated vesting

Helping fully separate grants for retention and grants for performance has been a good way drive the types of behavior you want to see on your teams -- and it's much simpler for employees to understand and teams to adminster.  Thank you for coming to my TED talk!