How does MFBF calculate the backflush qty ?

Dear Guru ,

How can i get the backflush quantity of the planned order ?

In our system , we created the planned order for the Finished Goods receipt via MFBF tcode .

In MFBF , we saw one field called 'Backflush qty' , Does someone can tell me how SAP calculate this quantity ?

Because we need an enhancement for this operation and we don't know SAP how to calculate ...

I checked in TABLE PLAF and found there have 2 fiels : GSMNG & AVMNG .

Is it the 'Backflush qty' = SMNG - AVMNG ???

I will appreciate if you can tell me the logic or send me the bapi that can calculate the 'Backflush qty' .

Many thanks .

Best Regards,

Carlos