New rate change date for Open enrollment

Summary: We have the rate start date set to 'Pay period start, before first check, on or after cover start'.
For 2027, the first pay period starts on 12/26/2026. We have new rates for Open 2027.
Our understanding is that since the rates are based on pay period start date, the new rate changes should be effective 12/26/2026 instead of 1/1/2027.
We tested a case where new rate is effective on 1/1/2027 and the system considered the new rate for Open 2027 eventhough the rate start date was 12/26/2026

Should we update the new rates as on 1/1/2027 or 12/26/2027? What is the usual approach in cases where rate is based on pay periods?