Amazon does it in dollars. Employees have a target comp figure in dollars, the annual stock refreshers are based on the price of the stock at that time, so if you got 100 units one year, and the stock doubles, all things being equal, you would only get 50 units the next year at refresh time.

In practice this means you can make good money off your hiring grant if price keeps going up, but you will also see your total comp hit a cliff / drop after a few years, since while stock going up is usually good, in Amazon's eyes, you've been lucky to be making more than your target comp those years and they aren't going to keep giving you the same amount of units if those units are worth more.