Hi
You are using NETWR as a filter. Please, check SAP Note 201830 - Calculation of the net price of an item for a proper understanding.
Because I believe you have run RV80HGEN. In the other hand, check following notes
SAP Note 326560 - Various problems when using VOFM functions
SAP Note 327220 - VOFM function and its objects
Check with your SD Consultant the settings in OVA8. Check also SAP Note 18613 - Checklist for Credit Management.
I hope this helps you
Regards
Eduardo