Freight on credit memo for returns PO

We are trying to achieve the below solution for a returns PO, created 2 condition types, assigned to the pricing procedure to achieve the GR posting. When we use MRRL to create a credit memo for both the material and the freight. the system creates a credit memo for the material and an invoice for the freight. Can someone tell me, what drives the credit memo generation for both freight and material

GR

Cr INV

Dr GRIR

Dr Freight clrg

Cr Freight

Credit Memo/ERS settlement/ MRRL

Dr Vendor

Cr GRIR

Cr Freight Clrg

We were able to create the GR side of the entry, using two other condition types on the PO.

Now when we do ERS settlement,

the system creates a credit memo for the INV line item and an invoice for the freight line item.

Both the freight and the material is charged to the PO vendor, we dont charge separate to the freight vendor at this point.

Any help will be appreciated.

Thanks