Defining criteria in a DMAX formula to be dynamic (top 5 list with database functions)

often times i create tables that are built for formulas to be dragged down. In one case I am doing a top 20 list of a database with set criteria of "group" and "month". I then search for the largest value, then I want the next largest value.

So I would like to use a DMAX formula (unless you can recommend another database function) where one of the criteria is dynamic, so that when I am looking for the second largest the criteria is that the the variable field must be less than the number above it.

Anyone have any ideas?