I was going to write a long post but I’ll keep it short.
You are first reviewed probably pretty fairly by your manager. Then the staff VP or VP will step in and reduce. All managers are allowed only 20% max of their team to get an exceeds. Your manager has no control so don’t blame them. VPs will usually push for their favorites to get higher ratings regardless of performance.
Your AIP is the same. Every manager is given a pool of dollars. For the past few years VP levels have asked managers to give back money from the pool so they can give to their favorites. The reduced pool is spread out, once again Staff VPs will step up and tell managers to reallocate. Also the AIP system will force anyone with exceeds to have a minimal 20% bigger AIP than anyone else.
Be grateful you still get an AIP. They are changing the rules every year.