Fixed amount condition changes depending on GR qty

Dear Experts,

Fixed amout condition is added in the Item - condition tab. Fixed value = $50.

Created PO for 100 qty with price per EA = 10. So, we expect the Invoice value to be 1000+50 = $1050.

But we did GR for 200 Qty. Since the condition type is fixed amount, we expected the delivery cost to be still $50 and total value to be 200 X10+50 = $2050

But, SAP calculations were different from what we expected. The fixed amout was changed as per the GR qty. and the PO total becomes $2100 (Fixed amount changed to 100 since GR qty = 2000)

Why the fixed amount doesnot remain fixed? How come the fixed amount increase depending on GR quantity?

Please suggest if there is any settings?

My confition type (ZFB3 has calc. type = B fixed).

Regards,

Shashidhar