Queries multiple fact tables at the same time

Validating my data model to ensure that existing report designs can be migrated to it, I've come across a report that includes measures at two different levels. Dimension A fully defines the grain of fact table A' and contributed to the grain of fact table P. Measures from fact table A' are presented as attributes of dimension A in a report that is primarily driven by fact table P. What's the proper solution for this -- add the measures from A' to A as attributes, or build the report to pull from multiple fact tables?

You can either query the two facts or build a new aggregate fact if performance is an issue.

You combine facts by summarizing each individually on common dimensions (or dimension attributes) and join the two aggregates.