If an employee’s rate after promotion or transfer is greater than the maximum rate of basic pay for the employee’s grade, that rate shall be treated as a retained rate under section
5363. The Office of Personnel Management shall prescribe by regulation the circumstances under which and the extent to which special rates under section
5305 (or similar provision of law) or locality-adjusted rates under section
5304 (or similar provision of law) are considered to be basic pay in applying this subsection.