ok, how about we look at things from a different perspective.
we know what we want, and the rules to get there, but either don't know how CR is deciding which records to display or physically can't because our requirements require too many reads of the data (if it is more than 2 it's too many...the main report and a subreport), so what I have found to be the simplest, most flexible solution is to not join my report to a database and read the tables.
So how do you get the data, stored procedures. I understand that not everyone knows how to create them, but they are worth the effort. You can do pretty much whatever you want and return only the columns that you want. You can place items into a table and update the values that you need to with whatever are the business rules for the report, and it is one hit to the database. Because of the flexiblity, I rarely need subreports...just have the stored proc return the values that you need in the row...then it is just a formatting issue.
so the short of it is, I would recommend writing a stored proc (if possible) as it will allow you to see your data and get the values that you need.
HTH