Hi
The documentation if the exit cab be seen in t code SMOD.
either the requirements class of those sales orders is not configured to calculate cost estimate or does not need to be valuated using that( fields Costing n Valuation in Req class)
Or the condition logic of your exit is preventing it. Just ensure that requirement class is same for both the sales orders, then we are sure its due to your custom logic in the exit which Abap needs to check
Ajay M