Schedule line proposed quantity for dependent material is more then required

Hi,

I have a BOM which consist of 4 subcontacting material as items.

When I run MRP, it creates schedule lines for the Header item, and all the dependent requirements are generated for child items.

However, the MRP proposed quantity of the child item is more than it should be required.

I have done manual calculation as well.

Product X

Child 1       MRP proposed -  144       Actual cal culation through BOM    ---  111

Child 2

Child 3

Child 4

What could be the possibilities. I have checked for scrap % in bom items, but its not maintained. Is LOT size calculation is the reason for this variance?