The FMV would be the sum of the cash value and the sum of the *additional* actuarial value provided by the rider. If the rider dictates the total value, I would expect that the FMV would be the total actuarial value (which would be greater than or equal to the cash balance) or, if the criteria in section 1.401(a)(9)-6 Q&A-12(c) to exclude the additional value are met, just the cash balance.
