Field "Origin of sales tax ID number" in billing header

Dear all,

i need to derive the VAT number by the KNAS segment of the payer. In customizing under Sales>Basic Functions>Taxes>Maintain Sales Tax Identification i can set up A and B. There are planty of explanations on SDN about that field to be the trigger and origin for the field content of the billing header field "Origin of sales tax ID number, VBRK-STCEG_H". Checking options of VBRK-STCEG_H you find 10 settings. But in customizing there are 2 settings only. I wanna ask how i can set up to get a specific entry of one out of those 10?

Would appreciate any hint.

Thanks in advance,

Andreas