You can set any corner of the table as fixed. The fixed corner will always keep its initial position during BOM update. When the table has been moved manually, the new position of this corner will be kept. Fixed corners allow to align BOM tables with other objects.
You may choose which corner to fix during the table placement by either the BMBOM command or the BOM manager; use the Tab key to cycle the corners. You can change the fixed corner of a BOM table in the BOM manager.