When using Multiple GUPs, the order in which they are entered makes no difference.
When using Multiple GUPs, the chosen GUP is based on if the SEP client is in the same subnet only. If Site B and Site B1 are on different subnets, then a client in Site B1 will never use the GUP in Site B. If they are in the same subnet however, the the GUP with the lowest IP address is used.
If you enable the Single GUP option, then this is only attempted after the client has failed to contact a Multiple GUP. The Single GUP option is essentially where the Backup GUP option moved in RU2.
As per the article I posted in your other thread, the order goes as below:
- Try Multiple GUPs
- Try Explicit GUPs
- Try Single GUP
- Try SEPM if allowed (if set to "Never Bypass" this step is not attempted)
http://www.symantec.com/docs/HOWTO81148
#EDIT#
Again (as per your other thread), if you want the GUP in site B to act as the failover update point for clients in Site B1 (i.e. if B1-GUP fails then use B-GUP), the you have to configure B-GUP as either an Explicit GUP or as a Single GUP in the LU policy assigned to the clients in Site B1. Assuming Site B and Site B1 are different subnets, then B-GUP will never be used by clients in Site B1 unless added as either an Explicit or Single GUP.