Journal approval

We are using version 11i and I would like to understand Journal Approval.  When the system checks the approval limits does it check by journal line absolute value or by the total of same accointing flexfields.  If by line number, which is what I am almost positive it does, is there a way to have the system compare the total in the batch ( either debits or credits) to the approval limits?  This is a SOX concern for auditors.  If by line number the preparer can enter multiple lines to by-pass the approval limit ccontrol.  Thanks you.