Hi Peter,
According to the SAP help, the PIRs are entered using the base unit of measure.
Independent requirements are created in Demand Management for all materials whose data has been transferred. These independent requirements are created in the base unit of measure of the material. The base unit of measure of the material is not necessarily the same as the base unit of measure of the information structure or the unit in which you planned the material.
Transfer to Demand Management - Sales & Operations Planning (LO-LIS-PLN) - SAP Library
Kind Regards,
Mariano