Call SQL Function With Multiple Parameters From C# Web Page?

I have an MS SQL function that is called with the following syntax: SELECT Field1, COUNT(*) AS RecordCount FROM GetDecileTable('WHERE ClientID = 7 AND LocationName = ''Default'' ', 10) The first parameter passes a specific WHERE clause that is used by the function for one of the internal queries. When I call this function in the front-end C# page, I need to send parameter values for the individual fields inside of the WHERE clause (in this example, both the ClientID & LocationName fields) The current C# code looks like this:

String SQLText = "SELECT Field1, COUNT(*) AS RecordCount FROM GetDecileTable('WHERE
ClientID = @ClientID AND LocationName = @LocationName ',10)";
SqlCommand Cmd = new SqlCommand(SQLText, SqlConnection);
Cmd.Parameters.Add("@ClientID", SqlDbType.Int).Value = 7; // Insert real ClientID
Cmd.Parameters.Add("@LocationName", SqlDbType.NVarChar(20)).Value = "Default";
// Real code uses Location Name from user input
SqlDataReader reader = Cmd.ExecuteReader();

When I do this, I get the following code from SQL profiler:

exec sp_executesql N'SELECT Field1, COUNT(*) as RecordCount FROM GetDecileTable
(''WHERE ClientID = @ClientID AND LocationName = @LocationName '',10)',
N'@ClientID int,@LocationID nvarchar(20)',
@ClientID=7,@LocationName=N'Default'

When this executes, SQL throws an error that it cannot parse past the first mention of @ClientID stating that the Scalar Variable @ClientID must be defined. If I modify the code to declare the variables first (see below), then I receive an error at the second mention of @ClientID that the variable already exists.

exec sp_executesql N'DECLARE @ClientID int; DECLARE @LocationName nvarchar(20);
SELECT Field1, COUNT(*) as RecordCount FROM GetDecileTable
(''WHERE ClientID = @ClientID AND LocationName = @LocationName '',10)',
N'@ClientID int,@LocationName nvarchar(20)',
@ClientID=7,@LocationName=N'Default'

I know that this method of adding parameters and calling SQL code from C# works well when I am selecting data from tables, but I am not sure how to embed parameters inside of the ' quote marks for the embedded WHERE clause being passed to the function.