Nz Or IIf(is Null) To Force A Certain Value?

I have a query in Access 2000 that I can't get to force a certain value in empty rows for a particular field column - maybe someone here can see why?

The SQL for the query is as follows (give or take some)...:

TRANSFORM Count([Testing DB].[DB_ID]) AS [CountOfDB_ID]
SELECT [Testing DB].State, [Location].[North], Count([Testing DB].[DB_ID]) AS [Total Of DB_ID]
FROM [Testing DB] LEFT JOIN [Location] ON [Testing DB].[Address] = [Location].Address
WHERE ((([Location].[Size])=Nz([Size],"Big")) AND (([Testing DB].[Window Length]) Is Not Null)
GROUP BY [Testing DB].State, [Location].[Size]
ORDER BY [Testing DB].State, [Location].[Size]
PIVOT Format([Date],"mmm-yyyy");

I want my crosstab to end up so that any records in the "Size" column that are not matched between the two tables, and therefore come up empty for those rows in the query results, are forced to change from empty to "Big" - so that they can be added into the count of "Big" hits that the query ends up with in the "Size" column. But all my "nz" addition did was remove the columns with blank values from the crosstab - no addition to the "Big" counts.

Am I perhaps going about this incorrectly? Maybe I should have used some form of iif(is null) instead.:confused: Any help is, as always, much appreciated.