Hi Halil,
Consider re-architecting the solution, using the 2LIS_03_BF and and 2LIS_03_UM datasources using cumulative (standard) key figures rather that non-cumulative key figures in the business content.
Skip using 2LIS-03_BX to initialize the inventory!
One can sum the _BF material document bases records and the _UM financial document revaluations from the beginning through now or a selected point in time to see the inventory at any point in time .
I promise that you match the values for MB5B exactly.
_BX can still be used to collect daily, weekly, or monthly snapshots for trend analysis if desired.
John Hawk