Annual increment (i.e merit increment) depends on your current grade, Performance Grade and CEP.

Two MX 12s with same performance grade can get different merit increment because of their CEP. This is where you can know where you stand relative to your peers.

I got a promoted last year to MX 11. I got 366 MI as a 'C' grader for this year. Don't know my CEP. Maybe MX 10, maybe MX 9.