RFFOUS_T in Pymt Methods in Country, but Variant maintained against RFFOEDI1

Hello Friends – We are sending ACH Payment details though Idocs. I see that Program RFFOUS_T in Pymt Methods in Country and Variant maintained against RFFOEDI1 in F110 and it is working fine.

My understanding is that if program (RFFOUS_T ) is maintained in Payment Methods in Country and Variant should be maintained against the same program (RFFOUS_T) in F110.

(1) Can you pls let me know in which scenario we maintain as above?

(2) Does not it work if Program maintained in Pymt Methods in Country - RFFOEDI1.

This set up is already in place and working fine. I just would like to understand the reason behind this.

Thanks