Usually, it seems like the rate of the purchase order lines would be populated to the corresponding item receipt lines.
when I try to give a particular fixed rate to a purchase order item line and then if I try to create an item receipt the exact rate will be carried over to the item recipe record.
and consider a case where we have set the item rate in purchase order but the total purchase order line amount is set as zero manually or if we apply a discount item that is of like 100 percent to that line then in that case if we create the item received to record the rate shown will be 0 . due to this behavior it seems like the purchase order rate is not directly populated to item receipt instead the purchase order line amount divided by the total quantity of that item being ordered in that purchase order and it is that value that is being populated in the rate field of item receipts.
In this case, the purchase order line amount total which is been discounted will also have tax amounts with them but in the case of the purchase order line total amount was manually modified to show as zero even though there is a rate in those cases the tax amount will not be populated to those lines.
And in case of the non-inventory items when been carried over to an item receipt it will have zero rate because for non inventory items there is no costing impact so in those cases the rate will be zero for those item types.