Core concepts
Accounts and statements are separate
An account mapping answers: Which group account should receive this local account’s transactions? A statement layout answers: Where should that group account appear in the report? Changing a statement layout does not remap source transactions. Changing an account mapping can change report values anywhere that group account is used.
Dimension hierarchy
The same separation applies to dimensions: local dimension items map to a group dimension item, and group dimension items can have their own parent in the hierarchy.

