Under smart split rules, permit one or more line items to be fixed, with the remaining balance (whatever it may be - variable) is allocated to one or more additional line items for different categories (one or more).

Rationale: Some line items may be recurring for the same amount, while some line items may be variable amounts, and there may even be some line items that only periodically appear.

It would be nice to have the option of allocating the remainder (whatever it may be) to one or more line items where the amount typically varies.