Grade Step Progression Salary determination date formula issue

Hi Fast Formula Experts:

Our business has biweekly payroll. Grade Step progression is trigging the grade step change accordingly based on the rules defined, however, when it comes salary update we are using a formula, which is not working as expected, its always defaulting to grade step update date. The ask here is if the grade step happens in the first week of the pay period, the salary update should happen on the first day of pay period. If the grade step update happens in the second week of pay period, salary should start on the first day of the second