Translation of Opening Balance Adjustment

Hi, can anyone direct me or advise as to how the opening balance adjustments are translated for historic accounts? We are in a situation where a historic account is being translated at the prior period average rate when we believe it should be using the effective rate from the prior period closing balance. There are previous period values and the consolidation % is 100% for the entity where we have the data. Are there any other situations where the prior period average balance would be used?

Thanks in advance