ATP suggesting different SSD for line with higher quantities even though it is in same ship set

Hi All,

We have a ATO sales order where 3 configured items are added as 3 lines. same ship set value is given for all the 3 lines.

First 2 lines are having lesser quantities as 360 and 840 but third line has 2400 as quantity. ATP has suggested a different scheduled ship date for the 3rd line (much delayed date) and the first 2 lines are having same date. So, even though all the lines are under same ship set, the third line with higher quantity has been given a different scheduled ship date.

When I created a similar order with same lines and when all the 3 lines were given less quantities, then the scheduled ship date was same for all the 3 lines which were under same ship set.