Multiple Dunning Letters

We are creating multiple dunning letters based upon entry type and reason but we also have a dunning letter which may go out to a customer at the same time as the 'normal' dunning letter. 

Since we have only two current levels, we were thinking of making this one letter a 2nd level rather than customizing .  Has anyone had this same predicament where 2 different phrase types would go

out on the same item to a customer? 

thank you