Do Task Related Accounting Sources Consider Task Rollup?

Summary:

When using Task related Accounting Sources (Task DFF in this case) to derive accounting for project costs, does SLA consider only the values of the Task the cost is charged to, or also the rollup of tasks?

We need to derive a segment value at the task level but do not want to have to manually populate the DFF on every task and sub-task we create that may have charges. Ideally we would like to only set the DFF at the highest task level and have it apply to all tasks below.