Person Selection Rule Not impacting on Participation Process: Grade Step

Hi

We need person selection rule to run "Participation Process: Grade Step". The scenario for person selection rule is that Employee increment is done after an year of his hiring. The month (in numeric value) in which his increment to be done is being saved on People screen DFF (e.g. 1 for 'Jan', 2 for 'Feb', 3 for 'March'  and so on) I created a database function which is having 2 parameters, Assignment Id and Effective Date and call in person selection rule formula. These 2 parameters are being passed from "formula function"  context value "Assignment ID", "Date Earned". If I