All persons employed in reduced worktime positions for partial service retirement pursuant to Sections 21110 through 21115 shall receive proportionally reduced compensation and, on a pro rata basis, all benefits customarily available to full-time employees of a public agency in similar classes or positions in accordance with the personnel policies of the public agency employer or pursuant to provisions of a memorandum of understanding reached pursuant to Chapter 10 (commencing with Section 3500) of Division 4 of Title 1.