WRX picking different GL based on general modification key

Hi,

Our client is procurring spare parts from different countries. So they maitained only one material type as Raw material and also only one valuation class. Hence our OBYC setting for BSX is valuation area,valuation class and GL account number, same time in WRX they have maintained Valuation area, General modification key and GL account number. Here GL account number is different based on the Places(countries)and also based on the general modification key. I want to know how system is picking different GRIR GL account number based on General modification key. Can anyone guide me on this.

govind.