Well there are solutions out there already for this, a base pay of x but a variable pay tied to employee performance (whatever metric they use e.g. tables waited on etc.) and a variable component tied to the company performance (profit sharing), perhaps even add an element of how long the employee worked there into this.

Make the data about what multiplier of base pay you paid out in the company performance variable component in the past few years and the upper and lower bounds of employee performance variable component and one gets the idea of how much they can make for sure and how much more they can potentially make it all goes well.