MC45 TCode Specs - Consumption Movements

Could anybody help with the design behind MC45 Consumption posting TCode. We are reverse engineering it trying to understand the logic. We have gotten pretty close, but are still missing a logic. So far we use tables

MSEG with SHKZG credit/debit indicator to define the credit/debit on DMBTR (Amount) with

Movement type in T156 where KZSTR = 2 and KZVBU is not null (gives only consumption movements from MSEG)

Postings from T156M with join on BUSTM where KZVBL is not null (gives only consumption postings based on BUSTM field)

But we are still off a little, I know I am missing an additional logic in the second step in to exclude/include only consumption posting line items.

Does anybody have any material on the design behind MC45. It's been a real challenge to reverse engineer this.

Thanks in Advance

Shruthi