Yeah, that's what I have previously experienced as well. However, I have tried a ton of different, all native fields, joined to the transaction record, e.g. Customer : Name/ID, Customer : Company Name, Customer : External ID, Account : Subsidiary, Account : Type, Department : Department Description, etc., etc. For all of them the "Show in Filter Region" option is grayed out. Only fields directly on the transaction record (i.e. not joined fields) seem to be able to be checked with that option. @Steven Scheppelman are you seeing something different?