Sort key required in Vendor Master & MIRO

Hi Guru,

I have assign sort key 014 PO number+ PO item in vendor master and and config using T-code OB16 , but when doing MIRO and save it is not showing in assignment field. It should be automatically assign.It is catching 00000

I have use following Field.

014 sortkey : Field - EBELN - Purchasing doc. no Length:10

Field- EBELP - Item Length:5

Can any one help me for this.