Hi,
If you want the MIRO price based on the price at the time of GR, maintain the price date category as 5 (GR date) in info record - purchase organization data 1 view, as shown below:
Once its maintained, create a new PO and test the scenario. Revert back in case of any issues.
You may refer the note: 457511 - FAQ: Purchase order change and goods receipt in purchasing
question number 3, for more details.
Regards,
AKPT