(5) Special limitation. If a defined benefit plan bases its normal retirement benefits on employee compensation, the compensation must reflect the compensation which would have been paid for a full year of participation within the meaning of section 411(b)(3). If an employee works less than a full year of participation, the compensation used to determine benefits under the plan for such year of participation must be multiplied by the ratio of the number of hours for a complete year of participation to the number of hours worked in such year. A plan whose benefit formula is computed on a computation base which cannot decrease is not required to adjust employee compensation in the manner described in the previous sentence. Thus, for example, if a plan provided a benefit based on an employee's compensation for his highest five consecutive years or a separate benefit for each year of participation based on the employee's compensation for such year the plan would not have to so adjust compensation. However, if a plan provided a benefit based on an employee's compensation for the employee's last five years or the five highest consecutive years out of the last 10 years, the compensation, would have to be so adjusted. For special rules for applying the limitations on proration of a year of participation for benefit accrual, see regulations prescribed by the Secretary of Labor under 29 CFR Part 2530, relating to minimum standards for employee pension benefit plans.