Hello @Adewunmi Agbato.
The inference engine and object-based tables mean you need to have an allocation line between both tables.
It would seem you already have PFS as an object in the model, otherwise you wouldn't be able to create the report for the drill-down . If so, creating the allocation line should be doable. Of course, you'd need to define PD as a model object. Then, you could define the allocation rule based on Project ID.
I'll see what I can concoct in my test environment, but it will be hard to reproduce yours, for sure!
(later)
I think this is somethink like what you wanted:

I put it together with the following model setup:
As described above, both PD and PFS are model objects, each with their Object ID.
The allocation line is really simple:

See that the Data Relationship is based on Project ID on both sides.
If you need more detail, I could write a longer article on the topic.
This post might be relevant as well (link).
#BillTheTBMGuy#CostingStandard(CT-Foundation)