Or a slight variant. Base salary grids, and confidential discretionary compensation.

Whatever gets negotiated on hiring in term of variable comp rolls off relatively quickly and then it's up to individual performance. Salary grids remove any curiosity, jealousy and other distractions on that topic for employees. It also avoids a negotiation on hiring, or leaving too much discretion to the employee making the hiring (and possible discrimination).

Lets you still reward performance while eliminating discrimination on hiring.